Adding cython v0.20.2 in third-party.

third_party/cython/src/Cython/Debugger/libpython.py

+#!/usr/bin/python
+
+# NOTE: this file is taken from the Python source distribution
+# It can be found under Tools/gdb/libpython.py. It is shipped with Cython
+# because it's not installed as a python module, and because changes are only
+# merged into new python versions (v3.2+).
+
+'''
+From gdb 7 onwards, gdb's build can be configured --with-python, allowing gdb
+to be extended with Python code e.g. for library-specific data visualizations,
+such as for the C++ STL types.  Documentation on this API can be seen at:
+http://sourceware.org/gdb/current/onlinedocs/gdb/Python-API.html
+
+
+This python module deals with the case when the process being debugged (the
+"inferior process" in gdb parlance) is itself python, or more specifically,
+linked against libpython.  In this situation, almost every item of data is a
+(PyObject*), and having the debugger merely print their addresses is not very
+enlightening.
+
+This module embeds knowledge about the implementation details of libpython so
+that we can emit useful visualizations e.g. a string, a list, a dict, a frame
+giving file/line information and the state of local variables
+
+In particular, given a gdb.Value corresponding to a PyObject* in the inferior
+process, we can generate a "proxy value" within the gdb process.  For example,
+given a PyObject* in the inferior process that is in fact a PyListObject*
+holding three PyObject* that turn out to be PyStringObject* instances, we can
+generate a proxy value within the gdb process that is a list of strings:
+  ["foo", "bar", "baz"]
+
+Doing so can be expensive for complicated graphs of objects, and could take
+some time, so we also have a "write_repr" method that writes a representation
+of the data to a file-like object.  This allows us to stop the traversal by
+having the file-like object raise an exception if it gets too much data.
+
+With both "proxyval" and "write_repr" we keep track of the set of all addresses
+visited so far in the traversal, to avoid infinite recursion due to cycles in
+the graph of object references.
+
+We try to defer gdb.lookup_type() invocations for python types until as late as
+possible: for a dynamically linked python binary, when the process starts in
+the debugger, the libpython.so hasn't been dynamically loaded yet, so none of
+the type names are known to the debugger
+
+The module also extends gdb with some python-specific commands.
+'''
+from __future__ import with_statement
+
+import os
+import re
+import sys
+import struct
+import locale
+import atexit
+import warnings
+import tempfile
+import textwrap
+import itertools
+
+import gdb
+
+if sys.version_info[0] < 3:
+    # I think this is the only way to fix this bug :'(
+    # http://sourceware.org/bugzilla/show_bug.cgi?id=12285
+    out, err = sys.stdout, sys.stderr
+    reload(sys).setdefaultencoding('UTF-8')
+    sys.stdout = out
+    sys.stderr = err
+
+# Look up the gdb.Type for some standard types:
+_type_char_ptr = gdb.lookup_type('char').pointer() # char*
+_type_unsigned_char_ptr = gdb.lookup_type('unsigned char').pointer()
+_type_void_ptr = gdb.lookup_type('void').pointer() # void*
+
+SIZEOF_VOID_P = _type_void_ptr.sizeof
+
+Py_TPFLAGS_HEAPTYPE = (1L << 9)
+
+Py_TPFLAGS_INT_SUBCLASS      = (1L << 23)
+Py_TPFLAGS_LONG_SUBCLASS     = (1L << 24)
+Py_TPFLAGS_LIST_SUBCLASS     = (1L << 25)
+Py_TPFLAGS_TUPLE_SUBCLASS    = (1L << 26)
+Py_TPFLAGS_STRING_SUBCLASS   = (1L << 27)
+Py_TPFLAGS_BYTES_SUBCLASS    = (1L << 27)
+Py_TPFLAGS_UNICODE_SUBCLASS  = (1L << 28)
+Py_TPFLAGS_DICT_SUBCLASS     = (1L << 29)
+Py_TPFLAGS_BASE_EXC_SUBCLASS = (1L << 30)
+Py_TPFLAGS_TYPE_SUBCLASS     = (1L << 31)
+
+MAX_OUTPUT_LEN = 1024
+
+hexdigits = "0123456789abcdef"
+
+ENCODING = locale.getpreferredencoding()
+
+class NullPyObjectPtr(RuntimeError):
+    pass
+
+
+def safety_limit(val):
+    # Given a integer value from the process being debugged, limit it to some
+    # safety threshold so that arbitrary breakage within said process doesn't
+    # break the gdb process too much (e.g. sizes of iterations, sizes of lists)
+    return min(val, 1000)
+
+
+def safe_range(val):
+    # As per range, but don't trust the value too much: cap it to a safety
+    # threshold in case the data was corrupted
+    return xrange(safety_limit(val))
+
+def write_unicode(file, text):
+    # Write a byte or unicode string to file. Unicode strings are encoded to
+    # ENCODING encoding with 'backslashreplace' error handler to avoid
+    # UnicodeEncodeError.
+    if isinstance(text, unicode):
+        text = text.encode(ENCODING, 'backslashreplace')
+    file.write(text)
+
+def os_fsencode(filename):
+    if not isinstance(filename, unicode):
+        return filename
+    encoding = sys.getfilesystemencoding()
+    if encoding == 'mbcs':
+        # mbcs doesn't support surrogateescape
+        return filename.encode(encoding)
+    encoded = []
+    for char in filename:
+        # surrogateescape error handler
+        if 0xDC80 <= ord(char) <= 0xDCFF:
+            byte = chr(ord(char) - 0xDC00)
+        else:
+            byte = char.encode(encoding)
+        encoded.append(byte)
+    return ''.join(encoded)
+
+class StringTruncated(RuntimeError):
+    pass
+
+class TruncatedStringIO(object):
+    '''Similar to cStringIO, but can truncate the output by raising a
+    StringTruncated exception'''
+    def __init__(self, maxlen=None):
+        self._val = ''
+        self.maxlen = maxlen
+
+    def write(self, data):
+        if self.maxlen:
+            if len(data) + len(self._val) > self.maxlen:
+                # Truncation:
+                self._val += data[0:self.maxlen - len(self._val)]
+                raise StringTruncated()
+
+        self._val += data
+
+    def getvalue(self):
+        return self._val
+
+
+# pretty printer lookup
+all_pretty_typenames = set()
+
+class PrettyPrinterTrackerMeta(type):
+
+    def __init__(self, name, bases, dict):
+        super(PrettyPrinterTrackerMeta, self).__init__(name, bases, dict)
+        all_pretty_typenames.add(self._typename)
+
+
+class PyObjectPtr(object):
+    """
+    Class wrapping a gdb.Value that's a either a (PyObject*) within the
+    inferior process, or some subclass pointer e.g. (PyStringObject*)
+
+    There will be a subclass for every refined PyObject type that we care
+    about.
+
+    Note that at every stage the underlying pointer could be NULL, point
+    to corrupt data, etc; this is the debugger, after all.
+    """
+
+    __metaclass__ = PrettyPrinterTrackerMeta
+
+    _typename = 'PyObject'
+
+    def __init__(self, gdbval, cast_to=None):
+        if cast_to:
+            self._gdbval = gdbval.cast(cast_to)
+        else:
+            self._gdbval = gdbval
+
+    def field(self, name):
+        '''
+        Get the gdb.Value for the given field within the PyObject, coping with
+        some python 2 versus python 3 differences.
+
+        Various libpython types are defined using the "PyObject_HEAD" and
+        "PyObject_VAR_HEAD" macros.
+
+        In Python 2, this these are defined so that "ob_type" and (for a var
+        object) "ob_size" are fields of the type in question.
+
+        In Python 3, this is defined as an embedded PyVarObject type thus:
+           PyVarObject ob_base;
+        so that the "ob_size" field is located insize the "ob_base" field, and
+        the "ob_type" is most easily accessed by casting back to a (PyObject*).
+        '''
+        if self.is_null():
+            raise NullPyObjectPtr(self)
+
+        if name == 'ob_type':
+            pyo_ptr = self._gdbval.cast(PyObjectPtr.get_gdb_type())
+            return pyo_ptr.dereference()[name]
+
+        if name == 'ob_size':
+            pyo_ptr = self._gdbval.cast(PyVarObjectPtr.get_gdb_type())
+            return pyo_ptr.dereference()[name]
+
+        # General case: look it up inside the object:
+        return self._gdbval.dereference()[name]
+
+    def pyop_field(self, name):
+        '''
+        Get a PyObjectPtr for the given PyObject* field within this PyObject,
+        coping with some python 2 versus python 3 differences.
+        '''
+        return PyObjectPtr.from_pyobject_ptr(self.field(name))
+
+    def write_field_repr(self, name, out, visited):
+        '''
+        Extract the PyObject* field named "name", and write its representation
+        to file-like object "out"
+        '''
+        field_obj = self.pyop_field(name)
+        field_obj.write_repr(out, visited)
+
+    def get_truncated_repr(self, maxlen):
+        '''
+        Get a repr-like string for the data, but truncate it at "maxlen" bytes
+        (ending the object graph traversal as soon as you do)
+        '''
+        out = TruncatedStringIO(maxlen)
+        try:
+            self.write_repr(out, set())
+        except StringTruncated:
+            # Truncation occurred:
+            return out.getvalue() + '...(truncated)'
+
+        # No truncation occurred:
+        return out.getvalue()
+
+    def type(self):
+        return PyTypeObjectPtr(self.field('ob_type'))
+
+    def is_null(self):
+        return 0 == long(self._gdbval)
+
+    def is_optimized_out(self):
+        '''
+        Is the value of the underlying PyObject* visible to the debugger?
+
+        This can vary with the precise version of the compiler used to build
+        Python, and the precise version of gdb.
+
+        See e.g. https://bugzilla.redhat.com/show_bug.cgi?id=556975 with
+        PyEval_EvalFrameEx's "f"
+        '''
+        return self._gdbval.is_optimized_out
+
+    def safe_tp_name(self):
+        try:
+            return self.type().field('tp_name').string()
+        except NullPyObjectPtr:
+            # NULL tp_name?
+            return 'unknown'
+        except RuntimeError:
+            # Can't even read the object at all?
+            return 'unknown'
+
+    def proxyval(self, visited):
+        '''
+        Scrape a value from the inferior process, and try to represent it
+        within the gdb process, whilst (hopefully) avoiding crashes when
+        the remote data is corrupt.
+
+        Derived classes will override this.
+
+        For example, a PyIntObject* with ob_ival 42 in the inferior process
+        should result in an int(42) in this process.
+
+        visited: a set of all gdb.Value pyobject pointers already visited
+        whilst generating this value (to guard against infinite recursion when
+        visiting object graphs with loops).  Analogous to Py_ReprEnter and
+        Py_ReprLeave
+        '''
+
+        class FakeRepr(object):
+            """
+            Class representing a non-descript PyObject* value in the inferior
+            process for when we don't have a custom scraper, intended to have
+            a sane repr().
+            """
+
+            def __init__(self, tp_name, address):
+                self.tp_name = tp_name
+                self.address = address
+
+            def __repr__(self):
+                # For the NULL pointer, we have no way of knowing a type, so
+                # special-case it as per
+                # http://bugs.python.org/issue8032#msg100882
+                if self.address == 0:
+                    return '0x0'
+                return '<%s at remote 0x%x>' % (self.tp_name, self.address)
+
+        return FakeRepr(self.safe_tp_name(),
+                        long(self._gdbval))
+
+    def write_repr(self, out, visited):
+        '''
+        Write a string representation of the value scraped from the inferior
+        process to "out", a file-like object.
+        '''
+        # Default implementation: generate a proxy value and write its repr
+        # However, this could involve a lot of work for complicated objects,
+        # so for derived classes we specialize this
+        return out.write(repr(self.proxyval(visited)))
+
+    @classmethod
+    def subclass_from_type(cls, t):
+        '''
+        Given a PyTypeObjectPtr instance wrapping a gdb.Value that's a
+        (PyTypeObject*), determine the corresponding subclass of PyObjectPtr
+        to use
+
+        Ideally, we would look up the symbols for the global types, but that
+        isn't working yet:
+          (gdb) python print gdb.lookup_symbol('PyList_Type')[0].value
+          Traceback (most recent call last):
+            File "<string>", line 1, in <module>
+          NotImplementedError: Symbol type not yet supported in Python scripts.
+          Error while executing Python code.
+
+        For now, we use tp_flags, after doing some string comparisons on the
+        tp_name for some special-cases that don't seem to be visible through
+        flags
+        '''
+        try:
+            tp_name = t.field('tp_name').string()
+            tp_flags = int(t.field('tp_flags'))
+        except RuntimeError:
+            # Handle any kind of error e.g. NULL ptrs by simply using the base
+            # class
+            return cls
+
+        #print 'tp_flags = 0x%08x' % tp_flags
+        #print 'tp_name = %r' % tp_name
+
+        name_map = {'bool': PyBoolObjectPtr,
+                    'classobj': PyClassObjectPtr,
+                    'instance': PyInstanceObjectPtr,
+                    'NoneType': PyNoneStructPtr,
+                    'frame': PyFrameObjectPtr,
+                    'set' : PySetObjectPtr,
+                    'frozenset' : PySetObjectPtr,
+                    'builtin_function_or_method' : PyCFunctionObjectPtr,
+                    }
+        if tp_name in name_map:
+            return name_map[tp_name]
+
+        if tp_flags & (Py_TPFLAGS_HEAPTYPE|Py_TPFLAGS_TYPE_SUBCLASS):
+            return PyTypeObjectPtr
+
+        if tp_flags & Py_TPFLAGS_INT_SUBCLASS:
+            return PyIntObjectPtr
+        if tp_flags & Py_TPFLAGS_LONG_SUBCLASS:
+            return PyLongObjectPtr
+        if tp_flags & Py_TPFLAGS_LIST_SUBCLASS:
+            return PyListObjectPtr
+        if tp_flags & Py_TPFLAGS_TUPLE_SUBCLASS:
+            return PyTupleObjectPtr
+        if tp_flags & Py_TPFLAGS_STRING_SUBCLASS:
+            try:
+                gdb.lookup_type('PyBytesObject')
+                return PyBytesObjectPtr
+            except RuntimeError:
+                return PyStringObjectPtr
+        if tp_flags & Py_TPFLAGS_UNICODE_SUBCLASS:
+            return PyUnicodeObjectPtr
+        if tp_flags & Py_TPFLAGS_DICT_SUBCLASS:
+            return PyDictObjectPtr
+        if tp_flags & Py_TPFLAGS_BASE_EXC_SUBCLASS:
+            return PyBaseExceptionObjectPtr
+
+        # Use the base class:
+        return cls
+
+    @classmethod
+    def from_pyobject_ptr(cls, gdbval):
+        '''
+        Try to locate the appropriate derived class dynamically, and cast
+        the pointer accordingly.
+        '''
+        try:
+            p = PyObjectPtr(gdbval)
+            cls = cls.subclass_from_type(p.type())
+            return cls(gdbval, cast_to=cls.get_gdb_type())
+        except RuntimeError, exc:
+            # Handle any kind of error e.g. NULL ptrs by simply using the base
+            # class
+            pass
+        return cls(gdbval)
+
+    @classmethod
+    def get_gdb_type(cls):
+        return gdb.lookup_type(cls._typename).pointer()
+
+    def as_address(self):
+        return long(self._gdbval)
+
+
+class PyVarObjectPtr(PyObjectPtr):
+    _typename = 'PyVarObject'
+
+class ProxyAlreadyVisited(object):
+    '''
+    Placeholder proxy to use when protecting against infinite recursion due to
+    loops in the object graph.
+
+    Analogous to the values emitted by the users of Py_ReprEnter and Py_ReprLeave
+    '''
+    def __init__(self, rep):
+        self._rep = rep
+
+    def __repr__(self):
+        return self._rep
+
+
+def _write_instance_repr(out, visited, name, pyop_attrdict, address):
+    '''Shared code for use by old-style and new-style classes:
+    write a representation to file-like object "out"'''
+    out.write('<')
+    out.write(name)
+
+    # Write dictionary of instance attributes:
+    if isinstance(pyop_attrdict, PyDictObjectPtr):
+        out.write('(')
+        first = True
+        for pyop_arg, pyop_val in pyop_attrdict.iteritems():
+            if not first:
+                out.write(', ')
+            first = False
+            out.write(pyop_arg.proxyval(visited))
+            out.write('=')
+            pyop_val.write_repr(out, visited)
+        out.write(')')
+    out.write(' at remote 0x%x>' % address)
+
+
+class InstanceProxy(object):
+
+    def __init__(self, cl_name, attrdict, address):
+        self.cl_name = cl_name
+        self.attrdict = attrdict
+        self.address = address
+
+    def __repr__(self):
+        if isinstance(self.attrdict, dict):
+            kwargs = ', '.join(["%s=%r" % (arg, val)
+                                for arg, val in self.attrdict.iteritems()])
+            return '<%s(%s) at remote 0x%x>' % (self.cl_name,
+                                                kwargs, self.address)
+        else:
+            return '<%s at remote 0x%x>' % (self.cl_name,
+                                            self.address)
+
+def _PyObject_VAR_SIZE(typeobj, nitems):
+    return ( ( typeobj.field('tp_basicsize') +
+               nitems * typeobj.field('tp_itemsize') +
+               (SIZEOF_VOID_P - 1)
+             ) & ~(SIZEOF_VOID_P - 1)
+           ).cast(gdb.lookup_type('size_t'))
+
+class PyTypeObjectPtr(PyObjectPtr):
+    _typename = 'PyTypeObject'
+
+    def get_attr_dict(self):
+        '''
+        Get the PyDictObject ptr representing the attribute dictionary
+        (or None if there's a problem)
+        '''
+        try:
+            typeobj = self.type()
+            dictoffset = int_from_int(typeobj.field('tp_dictoffset'))
+            if dictoffset != 0:
+                if dictoffset < 0:
+                    type_PyVarObject_ptr = gdb.lookup_type('PyVarObject').pointer()
+                    tsize = int_from_int(self._gdbval.cast(type_PyVarObject_ptr)['ob_size'])
+                    if tsize < 0:
+                        tsize = -tsize
+                    size = _PyObject_VAR_SIZE(typeobj, tsize)
+                    dictoffset += size
+                    assert dictoffset > 0
+                    assert dictoffset % SIZEOF_VOID_P == 0
+
+                dictptr = self._gdbval.cast(_type_char_ptr) + dictoffset
+                PyObjectPtrPtr = PyObjectPtr.get_gdb_type().pointer()
+                dictptr = dictptr.cast(PyObjectPtrPtr)
+                return PyObjectPtr.from_pyobject_ptr(dictptr.dereference())
+        except RuntimeError:
+            # Corrupt data somewhere; fail safe
+            pass
+
+        # Not found, or some kind of error:
+        return None
+
+    def proxyval(self, visited):
+        '''
+        Support for new-style classes.
+
+        Currently we just locate the dictionary using a transliteration to
+        python of _PyObject_GetDictPtr, ignoring descriptors
+        '''
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            return ProxyAlreadyVisited('<...>')
+        visited.add(self.as_address())
+
+        pyop_attr_dict = self.get_attr_dict()
+        if pyop_attr_dict:
+            attr_dict = pyop_attr_dict.proxyval(visited)
+        else:
+            attr_dict = {}
+        tp_name = self.safe_tp_name()
+
+        # New-style class:
+        return InstanceProxy(tp_name, attr_dict, long(self._gdbval))
+
+    def write_repr(self, out, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            out.write('<...>')
+            return
+        visited.add(self.as_address())
+
+        try:
+            tp_name = self.field('tp_name').string()
+        except RuntimeError:
+            tp_name = 'unknown'
+
+        out.write('<type %s at remote 0x%x>' % (tp_name,
+                                                self.as_address()))
+        # pyop_attrdict = self.get_attr_dict()
+        # _write_instance_repr(out, visited,
+                             # self.safe_tp_name(), pyop_attrdict, self.as_address())
+
+class ProxyException(Exception):
+    def __init__(self, tp_name, args):
+        self.tp_name = tp_name
+        self.args = args
+
+    def __repr__(self):
+        return '%s%r' % (self.tp_name, self.args)
+
+class PyBaseExceptionObjectPtr(PyObjectPtr):
+    """
+    Class wrapping a gdb.Value that's a PyBaseExceptionObject* i.e. an exception
+    within the process being debugged.
+    """
+    _typename = 'PyBaseExceptionObject'
+
+    def proxyval(self, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            return ProxyAlreadyVisited('(...)')
+        visited.add(self.as_address())
+        arg_proxy = self.pyop_field('args').proxyval(visited)
+        return ProxyException(self.safe_tp_name(),
+                              arg_proxy)
+
+    def write_repr(self, out, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            out.write('(...)')
+            return
+        visited.add(self.as_address())
+
+        out.write(self.safe_tp_name())
+        self.write_field_repr('args', out, visited)
+
+
+class PyClassObjectPtr(PyObjectPtr):
+    """
+    Class wrapping a gdb.Value that's a PyClassObject* i.e. a <classobj>
+    instance within the process being debugged.
+    """
+    _typename = 'PyClassObject'
+
+
+class BuiltInFunctionProxy(object):
+    def __init__(self, ml_name):
+        self.ml_name = ml_name
+
+    def __repr__(self):
+        return "<built-in function %s>" % self.ml_name
+
+class BuiltInMethodProxy(object):
+    def __init__(self, ml_name, pyop_m_self):
+        self.ml_name = ml_name
+        self.pyop_m_self = pyop_m_self
+
+    def __repr__(self):
+        return ('<built-in method %s of %s object at remote 0x%x>'
+                % (self.ml_name,
+                   self.pyop_m_self.safe_tp_name(),
+                   self.pyop_m_self.as_address())
+                )
+
+class PyCFunctionObjectPtr(PyObjectPtr):
+    """
+    Class wrapping a gdb.Value that's a PyCFunctionObject*
+    (see Include/methodobject.h and Objects/methodobject.c)
+    """
+    _typename = 'PyCFunctionObject'
+
+    def proxyval(self, visited):
+        m_ml = self.field('m_ml') # m_ml is a (PyMethodDef*)
+        ml_name = m_ml['ml_name'].string()
+
+        pyop_m_self = self.pyop_field('m_self')
+        if pyop_m_self.is_null():
+            return BuiltInFunctionProxy(ml_name)
+        else:
+            return BuiltInMethodProxy(ml_name, pyop_m_self)
+
+
+class PyCodeObjectPtr(PyObjectPtr):
+    """
+    Class wrapping a gdb.Value that's a PyCodeObject* i.e. a <code> instance
+    within the process being debugged.
+    """
+    _typename = 'PyCodeObject'
+
+    def addr2line(self, addrq):
+        '''
+        Get the line number for a given bytecode offset
+
+        Analogous to PyCode_Addr2Line; translated from pseudocode in
+        Objects/lnotab_notes.txt
+        '''
+        co_lnotab = self.pyop_field('co_lnotab').proxyval(set())
+
+        # Initialize lineno to co_firstlineno as per PyCode_Addr2Line
+        # not 0, as lnotab_notes.txt has it:
+        lineno = int_from_int(self.field('co_firstlineno'))
+
+        addr = 0
+        for addr_incr, line_incr in zip(co_lnotab[::2], co_lnotab[1::2]):
+            addr += ord(addr_incr)
+            if addr > addrq:
+                return lineno
+            lineno += ord(line_incr)
+        return lineno
+
+
+class PyDictObjectPtr(PyObjectPtr):
+    """
+    Class wrapping a gdb.Value that's a PyDictObject* i.e. a dict instance
+    within the process being debugged.
+    """
+    _typename = 'PyDictObject'
+
+    def iteritems(self):
+        '''
+        Yields a sequence of (PyObjectPtr key, PyObjectPtr value) pairs,
+        analagous to dict.iteritems()
+        '''
+        for i in safe_range(self.field('ma_mask') + 1):
+            ep = self.field('ma_table') + i
+            pyop_value = PyObjectPtr.from_pyobject_ptr(ep['me_value'])
+            if not pyop_value.is_null():
+                pyop_key = PyObjectPtr.from_pyobject_ptr(ep['me_key'])
+                yield (pyop_key, pyop_value)
+
+    def proxyval(self, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            return ProxyAlreadyVisited('{...}')
+        visited.add(self.as_address())
+
+        result = {}
+        for pyop_key, pyop_value in self.iteritems():
+            proxy_key = pyop_key.proxyval(visited)
+            proxy_value = pyop_value.proxyval(visited)
+            result[proxy_key] = proxy_value
+        return result
+
+    def write_repr(self, out, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            out.write('{...}')
+            return
+        visited.add(self.as_address())
+
+        out.write('{')
+        first = True
+        for pyop_key, pyop_value in self.iteritems():
+            if not first:
+                out.write(', ')
+            first = False
+            pyop_key.write_repr(out, visited)
+            out.write(': ')
+            pyop_value.write_repr(out, visited)
+        out.write('}')
+
+class PyInstanceObjectPtr(PyObjectPtr):
+    _typename = 'PyInstanceObject'
+
+    def proxyval(self, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            return ProxyAlreadyVisited('<...>')
+        visited.add(self.as_address())
+
+        # Get name of class:
+        in_class = self.pyop_field('in_class')
+        cl_name = in_class.pyop_field('cl_name').proxyval(visited)
+
+        # Get dictionary of instance attributes:
+        in_dict = self.pyop_field('in_dict').proxyval(visited)
+
+        # Old-style class:
+        return InstanceProxy(cl_name, in_dict, long(self._gdbval))
+
+    def write_repr(self, out, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            out.write('<...>')
+            return
+        visited.add(self.as_address())
+
+        # Old-style class:
+
+        # Get name of class:
+        in_class = self.pyop_field('in_class')
+        cl_name = in_class.pyop_field('cl_name').proxyval(visited)
+
+        # Get dictionary of instance attributes:
+        pyop_in_dict = self.pyop_field('in_dict')
+
+        _write_instance_repr(out, visited,
+                             cl_name, pyop_in_dict, self.as_address())
+
+class PyIntObjectPtr(PyObjectPtr):
+    _typename = 'PyIntObject'
+
+    def proxyval(self, visited):
+        result = int_from_int(self.field('ob_ival'))
+        return result
+
+class PyListObjectPtr(PyObjectPtr):
+    _typename = 'PyListObject'
+
+    def __getitem__(self, i):
+        # Get the gdb.Value for the (PyObject*) with the given index:
+        field_ob_item = self.field('ob_item')
+        return field_ob_item[i]
+
+    def proxyval(self, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            return ProxyAlreadyVisited('[...]')
+        visited.add(self.as_address())
+
+        result = [PyObjectPtr.from_pyobject_ptr(self[i]).proxyval(visited)
+                  for i in safe_range(int_from_int(self.field('ob_size')))]
+        return result
+
+    def write_repr(self, out, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            out.write('[...]')
+            return
+        visited.add(self.as_address())
+
+        out.write('[')
+        for i in safe_range(int_from_int(self.field('ob_size'))):
+            if i > 0:
+                out.write(', ')
+            element = PyObjectPtr.from_pyobject_ptr(self[i])
+            element.write_repr(out, visited)
+        out.write(']')
+
+class PyLongObjectPtr(PyObjectPtr):
+    _typename = 'PyLongObject'
+
+    def proxyval(self, visited):
+        '''
+        Python's Include/longobjrep.h has this declaration:
+           struct _longobject {
+               PyObject_VAR_HEAD
+               digit ob_digit[1];
+           };
+
+        with this description:
+            The absolute value of a number is equal to
+                 SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
+            Negative numbers are represented with ob_size < 0;
+            zero is represented by ob_size == 0.
+
+        where SHIFT can be either:
+            #define PyLong_SHIFT        30
+            #define PyLong_SHIFT        15
+        '''
+        ob_size = long(self.field('ob_size'))
+        if ob_size == 0:
+            return 0L
+
+        ob_digit = self.field('ob_digit')
+
+        if gdb.lookup_type('digit').sizeof == 2:
+            SHIFT = 15L
+        else:
+            SHIFT = 30L
+
+        digits = [long(ob_digit[i]) * 2**(SHIFT*i)
+                  for i in safe_range(abs(ob_size))]
+        result = sum(digits)
+        if ob_size < 0:
+            result = -result
+        return result
+
+    def write_repr(self, out, visited):
+        # Write this out as a Python 3 int literal, i.e. without the "L" suffix
+        proxy = self.proxyval(visited)
+        out.write("%s" % proxy)
+
+
+class PyBoolObjectPtr(PyLongObjectPtr):
+    """
+    Class wrapping a gdb.Value that's a PyBoolObject* i.e. one of the two
+    <bool> instances (Py_True/Py_False) within the process being debugged.
+    """
+    _typename = 'PyBoolObject'
+
+    def proxyval(self, visited):
+        castto = gdb.lookup_type('PyLongObject').pointer()
+        self._gdbval = self._gdbval.cast(castto)
+        return bool(PyLongObjectPtr(self._gdbval).proxyval(visited))
+
+
+class PyNoneStructPtr(PyObjectPtr):
+    """
+    Class wrapping a gdb.Value that's a PyObject* pointing to the
+    singleton (we hope) _Py_NoneStruct with ob_type PyNone_Type
+    """
+    _typename = 'PyObject'
+
+    def proxyval(self, visited):
+        return None
+
+
+class PyFrameObjectPtr(PyObjectPtr):
+    _typename = 'PyFrameObject'
+
+    def __init__(self, gdbval, cast_to=None):
+        PyObjectPtr.__init__(self, gdbval, cast_to)
+
+        if not self.is_optimized_out():
+            self.co = PyCodeObjectPtr.from_pyobject_ptr(self.field('f_code'))
+            self.co_name = self.co.pyop_field('co_name')
+            self.co_filename = self.co.pyop_field('co_filename')
+
+            self.f_lineno = int_from_int(self.field('f_lineno'))
+            self.f_lasti = int_from_int(self.field('f_lasti'))
+            self.co_nlocals = int_from_int(self.co.field('co_nlocals'))
+            self.co_varnames = PyTupleObjectPtr.from_pyobject_ptr(self.co.field('co_varnames'))
+
+    def iter_locals(self):
+        '''
+        Yield a sequence of (name,value) pairs of PyObjectPtr instances, for
+        the local variables of this frame
+        '''
+        if self.is_optimized_out():
+            return
+
+        f_localsplus = self.field('f_localsplus')
+        for i in safe_range(self.co_nlocals):
+            pyop_value = PyObjectPtr.from_pyobject_ptr(f_localsplus[i])
+            if not pyop_value.is_null():
+                pyop_name = PyObjectPtr.from_pyobject_ptr(self.co_varnames[i])
+                yield (pyop_name, pyop_value)
+
+    def iter_globals(self):
+        '''
+        Yield a sequence of (name,value) pairs of PyObjectPtr instances, for
+        the global variables of this frame
+        '''
+        if self.is_optimized_out():
+            return
+
+        pyop_globals = self.pyop_field('f_globals')
+        return pyop_globals.iteritems()
+
+    def iter_builtins(self):
+        '''
+        Yield a sequence of (name,value) pairs of PyObjectPtr instances, for
+        the builtin variables
+        '''
+        if self.is_optimized_out():
+            return
+
+        pyop_builtins = self.pyop_field('f_builtins')
+        return pyop_builtins.iteritems()
+
+    def get_var_by_name(self, name):
+        '''
+        Look for the named local variable, returning a (PyObjectPtr, scope) pair
+        where scope is a string 'local', 'global', 'builtin'
+
+        If not found, return (None, None)
+        '''
+        for pyop_name, pyop_value in self.iter_locals():
+            if name == pyop_name.proxyval(set()):
+                return pyop_value, 'local'
+        for pyop_name, pyop_value in self.iter_globals():
+            if name == pyop_name.proxyval(set()):
+                return pyop_value, 'global'
+        for pyop_name, pyop_value in self.iter_builtins():
+            if name == pyop_name.proxyval(set()):
+                return pyop_value, 'builtin'
+        return None, None
+
+    def filename(self):
+        '''Get the path of the current Python source file, as a string'''
+        if self.is_optimized_out():
+            return '(frame information optimized out)'
+        return self.co_filename.proxyval(set())
+
+    def current_line_num(self):
+        '''Get current line number as an integer (1-based)
+
+        Translated from PyFrame_GetLineNumber and PyCode_Addr2Line
+
+        See Objects/lnotab_notes.txt
+        '''
+        if self.is_optimized_out():
+            return None
+        f_trace = self.field('f_trace')
+        if long(f_trace) != 0:
+            # we have a non-NULL f_trace:
+            return self.f_lineno
+        else:
+            #try:
+            return self.co.addr2line(self.f_lasti)
+            #except ValueError:
+            #    return self.f_lineno
+
+    def current_line(self):
+        '''Get the text of the current source line as a string, with a trailing
+        newline character'''
+        if self.is_optimized_out():
+            return '(frame information optimized out)'
+        filename = self.filename()
+        with open(os_fsencode(filename), 'r') as f:
+            all_lines = f.readlines()
+            # Convert from 1-based current_line_num to 0-based list offset:
+            return all_lines[self.current_line_num()-1]
+
+    def write_repr(self, out, visited):
+        if self.is_optimized_out():
+            out.write('(frame information optimized out)')
+            return
+        out.write('Frame 0x%x, for file %s, line %i, in %s ('
+                  % (self.as_address(),
+                     self.co_filename.proxyval(visited),
+                     self.current_line_num(),
+                     self.co_name.proxyval(visited)))
+        first = True
+        for pyop_name, pyop_value in self.iter_locals():
+            if not first:
+                out.write(', ')
+            first = False
+
+            out.write(pyop_name.proxyval(visited))
+            out.write('=')
+            pyop_value.write_repr(out, visited)
+
+        out.write(')')
+
+class PySetObjectPtr(PyObjectPtr):
+    _typename = 'PySetObject'
+
+    def proxyval(self, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            return ProxyAlreadyVisited('%s(...)' % self.safe_tp_name())
+        visited.add(self.as_address())
+
+        members = []
+        table = self.field('table')
+        for i in safe_range(self.field('mask')+1):
+            setentry = table[i]
+            key = setentry['key']
+            if key != 0:
+                key_proxy = PyObjectPtr.from_pyobject_ptr(key).proxyval(visited)
+                if key_proxy != '<dummy key>':
+                    members.append(key_proxy)
+        if self.safe_tp_name() == 'frozenset':
+            return frozenset(members)
+        else:
+            return set(members)
+
+    def write_repr(self, out, visited):
+        # Emulate Python 3's set_repr
+        tp_name = self.safe_tp_name()
+
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            out.write('(...)')
+            return
+        visited.add(self.as_address())
+
+        # Python 3's set_repr special-cases the empty set:
+        if not self.field('used'):
+            out.write(tp_name)
+            out.write('()')
+            return
+
+        # Python 3 uses {} for set literals:
+        if tp_name != 'set':
+            out.write(tp_name)
+            out.write('(')
+
+        out.write('{')
+        first = True
+        table = self.field('table')
+        for i in safe_range(self.field('mask')+1):
+            setentry = table[i]
+            key = setentry['key']
+            if key != 0:
+                pyop_key = PyObjectPtr.from_pyobject_ptr(key)
+                key_proxy = pyop_key.proxyval(visited) # FIXME!
+                if key_proxy != '<dummy key>':
+                    if not first:
+                        out.write(', ')
+                    first = False
+                    pyop_key.write_repr(out, visited)
+        out.write('}')
+
+        if tp_name != 'set':
+            out.write(')')
+
+
+class PyBytesObjectPtr(PyObjectPtr):
+    _typename = 'PyBytesObject'
+
+    def __str__(self):
+        field_ob_size = self.field('ob_size')
+        field_ob_sval = self.field('ob_sval')
+        return ''.join(struct.pack('b', field_ob_sval[i])
+                           for i in safe_range(field_ob_size))
+
+    def proxyval(self, visited):
+        return str(self)
+
+    def write_repr(self, out, visited, py3=True):
+        # Write this out as a Python 3 bytes literal, i.e. with a "b" prefix
+
+        # Get a PyStringObject* within the Python 2 gdb process:
+        proxy = self.proxyval(visited)
+
+        # Transliteration of Python 3's Objects/bytesobject.c:PyBytes_Repr
+        # to Python 2 code:
+        quote = "'"
+        if "'" in proxy and not '"' in proxy:
+            quote = '"'
+
+        if py3:
+            out.write('b')
+
+        out.write(quote)
+        for byte in proxy:
+            if byte == quote or byte == '\\':
+                out.write('\\')
+                out.write(byte)
+            elif byte == '\t':
+                out.write('\\t')
+            elif byte == '\n':
+                out.write('\\n')
+            elif byte == '\r':
+                out.write('\\r')
+            elif byte < ' ' or ord(byte) >= 0x7f:
+                out.write('\\x')
+                out.write(hexdigits[(ord(byte) & 0xf0) >> 4])
+                out.write(hexdigits[ord(byte) & 0xf])
+            else:
+                out.write(byte)
+        out.write(quote)
+
+class PyStringObjectPtr(PyBytesObjectPtr):
+    _typename = 'PyStringObject'
+
+    def write_repr(self, out, visited):
+        return super(PyStringObjectPtr, self).write_repr(out, visited, py3=False)
+
+class PyTupleObjectPtr(PyObjectPtr):
+    _typename = 'PyTupleObject'
+
+    def __getitem__(self, i):
+        # Get the gdb.Value for the (PyObject*) with the given index:
+        field_ob_item = self.field('ob_item')
+        return field_ob_item[i]
+
+    def proxyval(self, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            return ProxyAlreadyVisited('(...)')
+        visited.add(self.as_address())
+
+        result = tuple([PyObjectPtr.from_pyobject_ptr(self[i]).proxyval(visited)
+                        for i in safe_range(int_from_int(self.field('ob_size')))])
+        return result
+
+    def write_repr(self, out, visited):
+        # Guard against infinite loops:
+        if self.as_address() in visited:
+            out.write('(...)')
+            return
+        visited.add(self.as_address())
+
+        out.write('(')
+        for i in safe_range(int_from_int(self.field('ob_size'))):
+            if i > 0:
+                out.write(', ')
+            element = PyObjectPtr.from_pyobject_ptr(self[i])
+            element.write_repr(out, visited)
+        if self.field('ob_size') == 1:
+            out.write(',)')
+        else:
+            out.write(')')
+
+
+def _unichr_is_printable(char):
+    # Logic adapted from Python 3's Tools/unicode/makeunicodedata.py
+    if char == u" ":
+        return True
+    import unicodedata
+    return unicodedata.category(char) not in ("C", "Z")
+
+if sys.maxunicode >= 0x10000:
+    _unichr = unichr
+else:
+    # Needed for proper surrogate support if sizeof(Py_UNICODE) is 2 in gdb
+    def _unichr(x):
+        if x < 0x10000:
+            return unichr(x)
+        x -= 0x10000
+        ch1 = 0xD800 | (x >> 10)
+        ch2 = 0xDC00 | (x & 0x3FF)
+        return unichr(ch1) + unichr(ch2)
+
+class PyUnicodeObjectPtr(PyObjectPtr):
+    _typename = 'PyUnicodeObject'
+
+    def char_width(self):
+        _type_Py_UNICODE = gdb.lookup_type('Py_UNICODE')
+        return _type_Py_UNICODE.sizeof
+
+    def proxyval(self, visited):
+        # From unicodeobject.h:
+        #     Py_ssize_t length;  /* Length of raw Unicode data in buffer */
+        #     Py_UNICODE *str;    /* Raw Unicode buffer */
+        field_length = long(self.field('length'))
+        field_str = self.field('str')
+
+        # Gather a list of ints from the Py_UNICODE array; these are either
+        # UCS-2 or UCS-4 code points:
+        if self.char_width() > 2:
+            Py_UNICODEs = [int(field_str[i]) for i in safe_range(field_length)]
+        else:
+            # A more elaborate routine if sizeof(Py_UNICODE) is 2 in the
+            # inferior process: we must join surrogate pairs.
+            Py_UNICODEs = []
+            i = 0
+            limit = safety_limit(field_length)
+            while i < limit:
+                ucs = int(field_str[i])
+                i += 1
+                if ucs < 0xD800 or ucs >= 0xDC00 or i == field_length:
+                    Py_UNICODEs.append(ucs)
+                    continue
+                # This could be a surrogate pair.
+                ucs2 = int(field_str[i])
+                if ucs2 < 0xDC00 or ucs2 > 0xDFFF:
+                    continue
+                code = (ucs & 0x03FF) << 10
+                code |= ucs2 & 0x03FF
+                code += 0x00010000
+                Py_UNICODEs.append(code)
+                i += 1
+
+        # Convert the int code points to unicode characters, and generate a
+        # local unicode instance.
+        # This splits surrogate pairs if sizeof(Py_UNICODE) is 2 here (in gdb).
+        result = u''.join([_unichr(ucs) for ucs in Py_UNICODEs])
+        return result
+
+    def write_repr(self, out, visited):
+        # Get a PyUnicodeObject* within the Python 2 gdb process:
+        proxy = self.proxyval(visited)
+
+        # Transliteration of Python 3's Object/unicodeobject.c:unicode_repr
+        # to Python 2:
+        try:
+            gdb.parse_and_eval('PyString_Type')
+        except RuntimeError:
+            # Python 3, don't write 'u' as prefix
+            pass
+        else:
+            # Python 2, write the 'u'
+            out.write('u')
+
+        if "'" in proxy and '"' not in proxy:
+            quote = '"'
+        else:
+            quote = "'"
+        out.write(quote)
+
+        i = 0
+        while i < len(proxy):
+            ch = proxy[i]
+            i += 1
+
+            # Escape quotes and backslashes
+            if ch == quote or ch == '\\':
+                out.write('\\')
+                out.write(ch)
+
+            #  Map special whitespace to '\t', \n', '\r'
+            elif ch == '\t':
+                out.write('\\t')
+            elif ch == '\n':
+                out.write('\\n')
+            elif ch == '\r':
+                out.write('\\r')
+
+            # Map non-printable US ASCII to '\xhh' */
+            elif ch < ' ' or ch == 0x7F:
+                out.write('\\x')
+                out.write(hexdigits[(ord(ch) >> 4) & 0x000F])
+                out.write(hexdigits[ord(ch) & 0x000F])
+
+            # Copy ASCII characters as-is
+            elif ord(ch) < 0x7F:
+                out.write(ch)
+
+            # Non-ASCII characters
+            else:
+                ucs = ch
+                ch2 = None
+                if sys.maxunicode < 0x10000:
+                    # If sizeof(Py_UNICODE) is 2 here (in gdb), join
+                    # surrogate pairs before calling _unichr_is_printable.
+                    if (i < len(proxy)
+                    and 0xD800 <= ord(ch) < 0xDC00 \
+                    and 0xDC00 <= ord(proxy[i]) <= 0xDFFF):
+                        ch2 = proxy[i]
+                        ucs = ch + ch2
+                        i += 1
+
+                # Unfortuately, Python 2's unicode type doesn't seem
+                # to expose the "isprintable" method
+                printable = _unichr_is_printable(ucs)
+                if printable:
+                    try:
+                        ucs.encode(ENCODING)
+                    except UnicodeEncodeError:
+                        printable = False
+
+                # Map Unicode whitespace and control characters
+                # (categories Z* and C* except ASCII space)
+                if not printable:
+                    if ch2 is not None:
+                        # Match Python 3's representation of non-printable
+                        # wide characters.
+                        code = (ord(ch) & 0x03FF) << 10
+                        code |= ord(ch2) & 0x03FF
+                        code += 0x00010000
+                    else:
+                        code = ord(ucs)
+
+                    # Map 8-bit characters to '\\xhh'
+                    if code <= 0xff:
+                        out.write('\\x')
+                        out.write(hexdigits[(code >> 4) & 0x000F])
+                        out.write(hexdigits[code & 0x000F])
+                    # Map 21-bit characters to '\U00xxxxxx'
+                    elif code >= 0x10000:
+                        out.write('\\U')
+                        out.write(hexdigits[(code >> 28) & 0x0000000F])
+                        out.write(hexdigits[(code >> 24) & 0x0000000F])
+                        out.write(hexdigits[(code >> 20) & 0x0000000F])
+                        out.write(hexdigits[(code >> 16) & 0x0000000F])
+                        out.write(hexdigits[(code >> 12) & 0x0000000F])
+                        out.write(hexdigits[(code >> 8) & 0x0000000F])
+                        out.write(hexdigits[(code >> 4) & 0x0000000F])
+                        out.write(hexdigits[code & 0x0000000F])
+                    # Map 16-bit characters to '\uxxxx'
+                    else:
+                        out.write('\\u')
+                        out.write(hexdigits[(code >> 12) & 0x000F])
+                        out.write(hexdigits[(code >> 8) & 0x000F])
+                        out.write(hexdigits[(code >> 4) & 0x000F])
+                        out.write(hexdigits[code & 0x000F])
+                else:
+                    # Copy characters as-is
+                    out.write(ch)
+                    if ch2 is not None:
+                        out.write(ch2)
+
+        out.write(quote)
+
+    def __unicode__(self):
+        return self.proxyval(set())
+
+    def __str__(self):
+        # In Python 3, everything is unicode (including attributes of e.g.
+        # code objects, such as function names). The Python 2 debugger code
+        # uses PyUnicodePtr objects to format strings etc, whereas with a
+        # Python 2 debuggee we'd get PyStringObjectPtr instances with __str__.
+        # Be compatible with that.
+        return unicode(self).encode('UTF-8')
+
+def int_from_int(gdbval):
+    return int(str(gdbval))
+
+
+def stringify(val):
+    # TODO: repr() puts everything on one line; pformat can be nicer, but
+    # can lead to v.long results; this function isolates the choice
+    if True:
+        return repr(val)
+    else:
+        from pprint import pformat
+        return pformat(val)
+
+
+class PyObjectPtrPrinter:
+    "Prints a (PyObject*)"
+
+    def __init__ (self, gdbval):
+        self.gdbval = gdbval
+
+    def to_string (self):
+        pyop = PyObjectPtr.from_pyobject_ptr(self.gdbval)
+        if True:
+            return pyop.get_truncated_repr(MAX_OUTPUT_LEN)
+        else:
+            # Generate full proxy value then stringify it.
+            # Doing so could be expensive
+            proxyval = pyop.proxyval(set())
+            return stringify(proxyval)
+
+def pretty_printer_lookup(gdbval):
+    type = gdbval.type.unqualified()
+    if type.code == gdb.TYPE_CODE_PTR:
+        type = type.target().unqualified()
+        if str(type) in all_pretty_typenames:
+            return PyObjectPtrPrinter(gdbval)
+
+"""
+During development, I've been manually invoking the code in this way:
+(gdb) python
+
+import sys
+sys.path.append('/home/david/coding/python-gdb')
+import libpython
+end
+
+then reloading it after each edit like this:
+(gdb) python reload(libpython)
+
+The following code should ensure that the prettyprinter is registered
+if the code is autoloaded by gdb when visiting libpython.so, provided
+that this python file is installed to the same path as the library (or its
+.debug file) plus a "-gdb.py" suffix, e.g:
+  /usr/lib/libpython2.6.so.1.0-gdb.py
+  /usr/lib/debug/usr/lib/libpython2.6.so.1.0.debug-gdb.py
+"""
+def register (obj):
+    if obj == None:
+        obj = gdb
+
+    # Wire up the pretty-printer
+    obj.pretty_printers.append(pretty_printer_lookup)
+
+register (gdb.current_objfile ())
+
+# Unfortunately, the exact API exposed by the gdb module varies somewhat
+# from build to build
+# See http://bugs.python.org/issue8279?#msg102276
+
+class Frame(object):
+    '''
+    Wrapper for gdb.Frame, adding various methods
+    '''
+    def __init__(self, gdbframe):
+        self._gdbframe = gdbframe
+
+    def older(self):
+        older = self._gdbframe.older()
+        if older:
+            return Frame(older)
+        else:
+            return None
+
+    def newer(self):
+        newer = self._gdbframe.newer()
+        if newer:
+            return Frame(newer)
+        else:
+            return None
+
+    def select(self):
+        '''If supported, select this frame and return True; return False if unsupported
+
+        Not all builds have a gdb.Frame.select method; seems to be present on Fedora 12
+        onwards, but absent on Ubuntu buildbot'''
+        if not hasattr(self._gdbframe, 'select'):
+            print ('Unable to select frame: '
+                   'this build of gdb does not expose a gdb.Frame.select method')
+            return False
+        self._gdbframe.select()
+        return True
+
+    def get_index(self):
+        '''Calculate index of frame, starting at 0 for the newest frame within
+        this thread'''
+        index = 0
+        # Go down until you reach the newest frame:
+        iter_frame = self
+        while iter_frame.newer():
+            index += 1
+            iter_frame = iter_frame.newer()
+        return index
+
+    def is_evalframeex(self):
+        '''Is this a PyEval_EvalFrameEx frame?'''
+        if self._gdbframe.name() == 'PyEval_EvalFrameEx':
+            '''
+            I believe we also need to filter on the inline
+            struct frame_id.inline_depth, only regarding frames with
+            an inline depth of 0 as actually being this function
+
+            So we reject those with type gdb.INLINE_FRAME
+            '''
+            if self._gdbframe.type() == gdb.NORMAL_FRAME:
+                # We have a PyEval_EvalFrameEx frame:
+                return True
+
+        return False
+
+    def read_var(self, varname):
+        """
+        read_var with respect to code blocks (gdbframe.read_var works with
+        respect to the most recent block)
+
+        Apparently this function doesn't work, though, as it seems to read
+        variables in other frames also sometimes.
+        """
+        block = self._gdbframe.block()
+        var = None
+
+        while block and var is None:
+            try:
+                var = self._gdbframe.read_var(varname, block)
+            except ValueError:
+                pass
+
+            block = block.superblock
+
+        return var
+
+    def get_pyop(self):
+        try:
+            # self.read_var does not always work properly, so select our frame
+            # and restore the previously selected frame
+            selected_frame = gdb.selected_frame()
+            self._gdbframe.select()
+            f = gdb.parse_and_eval('f')
+            selected_frame.select()
+        except RuntimeError:
+            return None
+        else:
+            return PyFrameObjectPtr.from_pyobject_ptr(f)
+
+    @classmethod
+    def get_selected_frame(cls):
+        _gdbframe = gdb.selected_frame()
+        if _gdbframe:
+            return Frame(_gdbframe)
+        return None
+
+    @classmethod
+    def get_selected_python_frame(cls):
+        '''Try to obtain the Frame for the python code in the selected frame,
+        or None'''
+        frame = cls.get_selected_frame()
+
+        while frame:
+            if frame.is_evalframeex():
+                return frame
+            frame = frame.older()
+
+        # Not found:
+        return None
+
+    def print_summary(self):
+        if self.is_evalframeex():
+            pyop = self.get_pyop()
+            if pyop:
+                line = pyop.get_truncated_repr(MAX_OUTPUT_LEN)
+                write_unicode(sys.stdout, '#%i %s\n' % (self.get_index(), line))
+                sys.stdout.write(pyop.current_line())
+            else:
+                sys.stdout.write('#%i (unable to read python frame information)\n' % self.get_index())
+        else:
+            sys.stdout.write('#%i\n' % self.get_index())
+
+class PyList(gdb.Command):
+    '''List the current Python source code, if any
+
+    Use
+       py-list START
+    to list at a different line number within the python source.
+
+    Use
+       py-list START, END
+    to list a specific range of lines within the python source.
+    '''
+
+    def __init__(self):
+        gdb.Command.__init__ (self,
+                              "py-list",
+                              gdb.COMMAND_FILES,
+                              gdb.COMPLETE_NONE)
+
+
+    def invoke(self, args, from_tty):
+        import re
+
+        start = None
+        end = None
+
+        m = re.match(r'\s*(\d+)\s*', args)
+        if m:
+            start = int(m.group(0))
+            end = start + 10
+
+        m = re.match(r'\s*(\d+)\s*,\s*(\d+)\s*', args)
+        if m:
+            start, end = map(int, m.groups())
+
+        frame = Frame.get_selected_python_frame()
+        if not frame:
+            print 'Unable to locate python frame'
+            return
+
+        pyop = frame.get_pyop()
+        if not pyop:
+            print 'Unable to read information on python frame'
+            return
+
+        filename = pyop.filename()
+        lineno = pyop.current_line_num()
+
+        if start is None:
+            start = lineno - 5
+            end = lineno + 5
+
+        if start<1:
+            start = 1
+
+        with open(os_fsencode(filename), 'r') as f:
+            all_lines = f.readlines()
+            # start and end are 1-based, all_lines is 0-based;
+            # so [start-1:end] as a python slice gives us [start, end] as a
+            # closed interval
+            for i, line in enumerate(all_lines[start-1:end]):
+                linestr = str(i+start)
+                # Highlight current line:
+                if i + start == lineno:
+                    linestr = '>' + linestr
+                sys.stdout.write('%4s    %s' % (linestr, line))
+
+
+# ...and register the command:
+PyList()
+
+def move_in_stack(move_up):
+    '''Move up or down the stack (for the py-up/py-down command)'''
+    frame = Frame.get_selected_python_frame()
+    while frame:
+        if move_up:
+            iter_frame = frame.older()
+        else:
+            iter_frame = frame.newer()
+
+        if not iter_frame:
+            break
+
+        if iter_frame.is_evalframeex():
+            # Result:
+            if iter_frame.select():
+                iter_frame.print_summary()
+            return
+
+        frame = iter_frame
+
+    if move_up:
+        print 'Unable to find an older python frame'
+    else:
+        print 'Unable to find a newer python frame'
+
+class PyUp(gdb.Command):
+    'Select and print the python stack frame that called this one (if any)'
+    def __init__(self):
+        gdb.Command.__init__ (self,
+                              "py-up",
+                              gdb.COMMAND_STACK,
+                              gdb.COMPLETE_NONE)
+
+
+    def invoke(self, args, from_tty):
+        move_in_stack(move_up=True)
+
+class PyDown(gdb.Command):
+    'Select and print the python stack frame called by this one (if any)'
+    def __init__(self):
+        gdb.Command.__init__ (self,
+                              "py-down",
+                              gdb.COMMAND_STACK,
+                              gdb.COMPLETE_NONE)
+
+
+    def invoke(self, args, from_tty):
+        move_in_stack(move_up=False)
+
+# Not all builds of gdb have gdb.Frame.select
+if hasattr(gdb.Frame, 'select'):
+    PyUp()
+    PyDown()
+
+class PyBacktrace(gdb.Command):
+    'Display the current python frame and all the frames within its call stack (if any)'
+    def __init__(self):
+        gdb.Command.__init__ (self,
+                              "py-bt",
+                              gdb.COMMAND_STACK,
+                              gdb.COMPLETE_NONE)
+
+
+    def invoke(self, args, from_tty):
+        frame = Frame.get_selected_python_frame()
+        while frame:
+            if frame.is_evalframeex():
+                frame.print_summary()
+            frame = frame.older()
+
+PyBacktrace()
+
+class PyPrint(gdb.Command):
+    'Look up the given python variable name, and print it'
+    def __init__(self):
+        gdb.Command.__init__ (self,
+                              "py-print",
+                              gdb.COMMAND_DATA,
+                              gdb.COMPLETE_NONE)
+
+
+    def invoke(self, args, from_tty):
+        name = str(args)
+
+        frame = Frame.get_selected_python_frame()
+        if not frame:
+            print 'Unable to locate python frame'
+            return
+
+        pyop_frame = frame.get_pyop()
+        if not pyop_frame:
+            print 'Unable to read information on python frame'
+            return
+
+        pyop_var, scope = pyop_frame.get_var_by_name(name)
+
+        if pyop_var:
+            print ('%s %r = %s'
+                   % (scope,
+                      name,
+                      pyop_var.get_truncated_repr(MAX_OUTPUT_LEN)))
+        else:
+            print '%r not found' % name
+
+PyPrint()
+
+class PyLocals(gdb.Command):
+    'Look up the given python variable name, and print it'
+
+    def invoke(self, args, from_tty):
+        name = str(args)
+
+        frame = Frame.get_selected_python_frame()
+        if not frame:
+            print 'Unable to locate python frame'
+            return
+
+        pyop_frame = frame.get_pyop()
+        if not pyop_frame:
+            print 'Unable to read information on python frame'
+            return
+
+        namespace = self.get_namespace(pyop_frame)
+        namespace = [(name.proxyval(set()), val) for name, val in namespace]
+
+        if namespace:
+            name, val = max(namespace, key=lambda (name, val): len(name))
+            max_name_length = len(name)
+
+            for name, pyop_value in namespace:
+                value = pyop_value.get_truncated_repr(MAX_OUTPUT_LEN)
+                print ('%-*s = %s' % (max_name_length, name, value))
+
+    def get_namespace(self, pyop_frame):
+        return pyop_frame.iter_locals()
+
+
+class PyGlobals(PyLocals):
+    'List all the globals in the currently select Python frame'
+
+    def get_namespace(self, pyop_frame):
+        return pyop_frame.iter_globals()
+
+
+PyLocals("py-locals", gdb.COMMAND_DATA, gdb.COMPLETE_NONE)
+PyGlobals("py-globals", gdb.COMMAND_DATA, gdb.COMPLETE_NONE)
+
+
+class PyNameEquals(gdb.Function):
+
+    def _get_pycurframe_attr(self, attr):
+        frame = Frame(gdb.selected_frame())
+        if frame.is_evalframeex():
+            pyframe = frame.get_pyop()
+            if pyframe is None:
+                warnings.warn("Use a Python debug build, Python breakpoints "
+                              "won't work otherwise.")
+                return None
+
+            return getattr(pyframe, attr).proxyval(set())
+
+        return None
+
+    def invoke(self, funcname):
+        attr = self._get_pycurframe_attr('co_name')
+        return attr is not None and attr == funcname.string()
+
+PyNameEquals("pyname_equals")
+
+
+class PyModEquals(PyNameEquals):
+
+    def invoke(self, modname):
+        attr = self._get_pycurframe_attr('co_filename')
+        if attr is not None:
+            filename, ext = os.path.splitext(os.path.basename(attr))
+            return filename == modname.string()
+        return False
+
+PyModEquals("pymod_equals")
+
+
+class PyBreak(gdb.Command):
+    """
+    Set a Python breakpoint. Examples:
+
+    Break on any function or method named 'func' in module 'modname'
+
+        py-break modname.func
+
+    Break on any function or method named 'func'
+
+        py-break func
+    """
+
+    def invoke(self, funcname, from_tty):
+        if '.' in funcname:
+            modname, dot, funcname = funcname.rpartition('.')
+            cond = '$pyname_equals("%s") && $pymod_equals("%s")' % (funcname,
+                                                                    modname)
+        else:
+            cond = '$pyname_equals("%s")' % funcname
+
+        gdb.execute('break PyEval_EvalFrameEx if ' + cond)
+
+PyBreak("py-break", gdb.COMMAND_RUNNING, gdb.COMPLETE_NONE)
+
+
+class _LoggingState(object):
+    """
+    State that helps to provide a reentrant gdb.execute() function.
+    """
+
+    def __init__(self):
+        self.fd, self.filename = tempfile.mkstemp()
+        self.file = os.fdopen(self.fd, 'r+')
+        _execute("set logging file %s" % self.filename)
+        self.file_position_stack = []
+
+        atexit.register(os.close, self.fd)
+        atexit.register(os.remove, self.filename)
+
+    def __enter__(self):
+        if not self.file_position_stack:
+            _execute("set logging redirect on")
+            _execute("set logging on")
+            _execute("set pagination off")
+
+        self.file_position_stack.append(os.fstat(self.fd).st_size)
+        return self
+
+    def getoutput(self):
+        gdb.flush()
+        self.file.seek(self.file_position_stack[-1])
+        result = self.file.read()
+        return result
+
+    def __exit__(self, exc_type, exc_val, tb):
+        startpos = self.file_position_stack.pop()
+        self.file.seek(startpos)
+        self.file.truncate()
+        if not self.file_position_stack:
+            _execute("set logging off")
+            _execute("set logging redirect off")
+            _execute("set pagination on")
+
+
+def execute(command, from_tty=False, to_string=False):
+    """
+    Replace gdb.execute() with this function and have it accept a 'to_string'
+    argument (new in 7.2). Have it properly capture stderr also. Ensure
+    reentrancy.
+    """
+    if to_string:
+        with _logging_state as state:
+            _execute(command, from_tty)
+            return state.getoutput()
+    else:
+        _execute(command, from_tty)
+
+
+_execute = gdb.execute
+gdb.execute = execute
+_logging_state = _LoggingState()
+
+
+def get_selected_inferior():
+    """
+    Return the selected inferior in gdb.
+    """
+    # Woooh, another bug in gdb! Is there an end in sight?
+    # http://sourceware.org/bugzilla/show_bug.cgi?id=12212
+    return gdb.inferiors()[0]
+
+    selected_thread = gdb.selected_thread()
+
+    for inferior in gdb.inferiors():
+        for thread in inferior.threads():
+            if thread == selected_thread:
+                return inferior
+
+def source_gdb_script(script_contents, to_string=False):
+    """
+    Source a gdb script with script_contents passed as a string. This is useful
+    to provide defines for py-step and py-next to make them repeatable (this is
+    not possible with gdb.execute()). See
+    http://sourceware.org/bugzilla/show_bug.cgi?id=12216
+    """
+    fd, filename = tempfile.mkstemp()
+    f = os.fdopen(fd, 'w')
+    f.write(script_contents)
+    f.close()
+    gdb.execute("source %s" % filename, to_string=to_string)
+    os.remove(filename)
+
+def register_defines():
+    source_gdb_script(textwrap.dedent("""\
+        define py-step
+        -py-step
+        end
+
+        define py-next
+        -py-next
+        end
+
+        document py-step
+        %s
+        end
+
+        document py-next
+        %s
+        end
+    """) % (PyStep.__doc__, PyNext.__doc__))
+
+
+def stackdepth(frame):
+    "Tells the stackdepth of a gdb frame."
+    depth = 0
+    while frame:
+        frame = frame.older()
+        depth += 1
+
+    return depth
+
+class ExecutionControlCommandBase(gdb.Command):
+    """
+    Superclass for language specific execution control. Language specific
+    features should be implemented by lang_info using the LanguageInfo
+    interface. 'name' is the name of the command.
+    """
+
+    def __init__(self, name, lang_info):
+        super(ExecutionControlCommandBase, self).__init__(
+                                name, gdb.COMMAND_RUNNING, gdb.COMPLETE_NONE)
+        self.lang_info = lang_info
+
+    def install_breakpoints(self):
+        all_locations = itertools.chain(
+            self.lang_info.static_break_functions(),
+            self.lang_info.runtime_break_functions())
+
+        for location in all_locations:
+            result = gdb.execute('break %s' % location, to_string=True)
+            yield re.search(r'Breakpoint (\d+)', result).group(1)
+
+    def delete_breakpoints(self, breakpoint_list):
+        for bp in breakpoint_list:
+            gdb.execute("delete %s" % bp)
+
+    def filter_output(self, result):
+        reflags = re.MULTILINE
+
+        output_on_halt = [
+            (r'^Program received signal .*', reflags|re.DOTALL),
+            (r'.*[Ww]arning.*', 0),
+            (r'^Program exited .*', reflags),
+        ]
+
+        output_always = [
+            # output when halting on a watchpoint
+            (r'^(Old|New) value = .*', reflags),
+            # output from the 'display' command
+            (r'^\d+: \w+ = .*', reflags),
+        ]
+
+        def filter_output(regexes):
+            output = []
+            for regex, flags in regexes:
+                for match in re.finditer(regex, result, flags):
+                    output.append(match.group(0))
+
+            return '\n'.join(output)
+
+        # Filter the return value output of the 'finish' command
+        match_finish = re.search(r'^Value returned is \$\d+ = (.*)', result,
+                                 re.MULTILINE)
+        if match_finish:
+            finish_output = 'Value returned: %s\n' % match_finish.group(1)
+        else:
+            finish_output = ''
+
+        return (filter_output(output_on_halt),
+                finish_output + filter_output(output_always))
+
+
+    def stopped(self):
+        return get_selected_inferior().pid == 0
+
+    def finish_executing(self, result):
+        """
+        After doing some kind of code running in the inferior, print the line
+        of source code or the result of the last executed gdb command (passed
+        in as the `result` argument).
+        """
+        output_on_halt, output_always = self.filter_output(result)
+
+        if self.stopped():
+            print output_always
+            print output_on_halt
+        else:
+            frame = gdb.selected_frame()
+            source_line = self.lang_info.get_source_line(frame)
+            if self.lang_info.is_relevant_function(frame):
+                raised_exception = self.lang_info.exc_info(frame)
+                if raised_exception:
+                    print raised_exception
+
+            if source_line:
+                if output_always.rstrip():
+                    print output_always.rstrip()
+                print source_line
+            else:
+                print result
+
+    def _finish(self):
+        """
+        Execute until the function returns (or until something else makes it
+        stop)
+        """
+        if gdb.selected_frame().older() is not None:
+            return gdb.execute('finish', to_string=True)
+        else:
+            # outermost frame, continue
+            return gdb.execute('cont', to_string=True)
+
+    def _finish_frame(self):
+        """
+        Execute until the function returns to a relevant caller.
+        """
+        while True:
+            result = self._finish()
+
+            try:
+                frame = gdb.selected_frame()
+            except RuntimeError:
+                break
+
+            hitbp = re.search(r'Breakpoint (\d+)', result)
+            is_relevant = self.lang_info.is_relevant_function(frame)
+            if hitbp or is_relevant or self.stopped():
+                break
+
+        return result
+
+    def finish(self, *args):
+        "Implements the finish command."
+        result = self._finish_frame()
+        self.finish_executing(result)
+
+    def step(self, stepinto, stepover_command='next'):
+        """
+        Do a single step or step-over. Returns the result of the last gdb
+        command that made execution stop.
+
+        This implementation, for stepping, sets (conditional) breakpoints for
+        all functions that are deemed relevant. It then does a step over until
+        either something halts execution, or until the next line is reached.
+
+        If, however, stepover_command is given, it should be a string gdb
+        command that continues execution in some way. The idea is that the
+        caller has set a (conditional) breakpoint or watchpoint that can work
+        more efficiently than the step-over loop. For Python this means setting
+        a watchpoint for f->f_lasti, which means we can then subsequently
+        "finish" frames.
+        We want f->f_lasti instead of f->f_lineno, because the latter only
+        works properly with local trace functions, see
+        PyFrameObjectPtr.current_line_num and PyFrameObjectPtr.addr2line.
+        """
+        if stepinto:
+            breakpoint_list = list(self.install_breakpoints())
+
+        beginframe = gdb.selected_frame()
+
+        if self.lang_info.is_relevant_function(beginframe):
+            # If we start in a relevant frame, initialize stuff properly. If
+            # we don't start in a relevant frame, the loop will halt
+            # immediately. So don't call self.lang_info.lineno() as it may
+            # raise for irrelevant frames.
+            beginline = self.lang_info.lineno(beginframe)
+
+            if not stepinto:
+                depth = stackdepth(beginframe)
+
+        newframe = beginframe
+
+        while True:
+            if self.lang_info.is_relevant_function(newframe):
+                result = gdb.execute(stepover_command, to_string=True)
+            else:
+                result = self._finish_frame()
+
+            if self.stopped():
+                break
+
+            newframe = gdb.selected_frame()
+            is_relevant_function = self.lang_info.is_relevant_function(newframe)
+            try:
+                framename = newframe.name()
+            except RuntimeError:
+                framename = None
+
+            m = re.search(r'Breakpoint (\d+)', result)
+            if m:
+                if is_relevant_function and m.group(1) in breakpoint_list:
+                    # although we hit a breakpoint, we still need to check
+                    # that the function, in case hit by a runtime breakpoint,
+                    # is in the right context
+                    break
+
+            if newframe != beginframe:
+                # new function
+
+                if not stepinto:
+                    # see if we returned to the caller
+                    newdepth = stackdepth(newframe)
+                    is_relevant_function = (newdepth < depth and
+                                            is_relevant_function)
+
+                if is_relevant_function:
+                    break
+            else:
+                # newframe equals beginframe, check for a difference in the
+                # line number
+                lineno = self.lang_info.lineno(newframe)
+                if lineno and lineno != beginline:
+                    break
+
+        if stepinto:
+            self.delete_breakpoints(breakpoint_list)
+
+        self.finish_executing(result)
+
+    def run(self, args, from_tty):
+        self.finish_executing(gdb.execute('run ' + args, to_string=True))
+
+    def cont(self, *args):
+        self.finish_executing(gdb.execute('cont', to_string=True))
+
+
+class LanguageInfo(object):
+    """
+    This class defines the interface that ExecutionControlCommandBase needs to
+    provide language-specific execution control.
+
+    Classes that implement this interface should implement:
+
+        lineno(frame)
+            Tells the current line number (only called for a relevant frame).
+            If lineno is a false value it is not checked for a difference.
+
+        is_relevant_function(frame)
+            tells whether we care about frame 'frame'
+
+        get_source_line(frame)
+            get the line of source code for the current line (only called for a
+            relevant frame). If the source code cannot be retrieved this
+            function should return None
+
+        exc_info(frame) -- optional
+            tells whether an exception was raised, if so, it should return a
+            string representation of the exception value, None otherwise.
+
+        static_break_functions()
+            returns an iterable of function names that are considered relevant
+            and should halt step-into execution. This is needed to provide a
+            performing step-into
+
+        runtime_break_functions() -- optional
+            list of functions that we should break into depending on the
+            context
+    """
+
+    def exc_info(self, frame):
+        "See this class' docstring."
+
+    def runtime_break_functions(self):
+        """
+        Implement this if the list of step-into functions depends on the
+        context.
+        """
+        return ()
+
+class PythonInfo(LanguageInfo):
+
+    def pyframe(self, frame):
+        pyframe = Frame(frame).get_pyop()
+        if pyframe:
+            return pyframe
+        else:
+            raise gdb.RuntimeError(
+                "Unable to find the Python frame, run your code with a debug "
+                "build (configure with --with-pydebug or compile with -g).")
+
+    def lineno(self, frame):
+        return self.pyframe(frame).current_line_num()
+
+    def is_relevant_function(self, frame):
+        return Frame(frame).is_evalframeex()
+
+    def get_source_line(self, frame):
+        try:
+            pyframe = self.pyframe(frame)
+            return '%4d    %s' % (pyframe.current_line_num(),
+                                  pyframe.current_line().rstrip())
+        except IOError, e:
+            return None
+
+    def exc_info(self, frame):
+        try:
+            tstate = frame.read_var('tstate').dereference()
+            if gdb.parse_and_eval('tstate->frame == f'):
+                # tstate local variable initialized, check for an exception
+                inf_type = tstate['curexc_type']
+                inf_value = tstate['curexc_value']
+
+                if inf_type:
+                    return 'An exception was raised: %s' % (inf_value,)
+        except (ValueError, RuntimeError), e:
+            # Could not read the variable tstate or it's memory, it's ok
+            pass
+
+    def static_break_functions(self):
+        yield 'PyEval_EvalFrameEx'
+
+
+class PythonStepperMixin(object):
+    """
+    Make this a mixin so CyStep can also inherit from this and use a
+    CythonCodeStepper at the same time.
+    """
+
+    def python_step(self, stepinto):
+        """
+        Set a watchpoint on the Python bytecode instruction pointer and try
+        to finish the frame
+        """
+        output = gdb.execute('watch f->f_lasti', to_string=True)
+        watchpoint = int(re.search(r'[Ww]atchpoint (\d+):', output).group(1))
+        self.step(stepinto=stepinto, stepover_command='finish')
+        gdb.execute('delete %s' % watchpoint)
+
+
+class PyStep(ExecutionControlCommandBase, PythonStepperMixin):
+    "Step through Python code."
+
+    stepinto = True
+
+    def invoke(self, args, from_tty):
+        self.python_step(stepinto=self.stepinto)
+
+class PyNext(PyStep):
+    "Step-over Python code."
+
+    stepinto = False
+
+class PyFinish(ExecutionControlCommandBase):
+    "Execute until function returns to a caller."
+
+    invoke = ExecutionControlCommandBase.finish
+
+class PyRun(ExecutionControlCommandBase):
+    "Run the program."
+
+    invoke = ExecutionControlCommandBase.run
+
+class PyCont(ExecutionControlCommandBase):
+
+    invoke = ExecutionControlCommandBase.cont
+
+
+def _pointervalue(gdbval):
+    """
+    Return the value of the pionter as a Python int.
+
+    gdbval.type must be a pointer type
+    """
+    # don't convert with int() as it will raise a RuntimeError
+    if gdbval.address is not None:
+        return long(gdbval.address)
+    else:
+        # the address attribute is None sometimes, in which case we can
+        # still convert the pointer to an int
+        return long(gdbval)
+
+def pointervalue(gdbval):
+    pointer = _pointervalue(gdbval)
+    try:
+        if pointer < 0:
+            raise gdb.GdbError("Negative pointer value, presumably a bug "
+                               "in gdb, aborting.")
+    except RuntimeError:
+        # work around yet another bug in gdb where you get random behaviour
+        # and tracebacks
+        pass
+
+    return pointer
+
+def get_inferior_unicode_postfix():
+    try:
+        gdb.parse_and_eval('PyUnicode_FromEncodedObject')
+    except RuntimeError:
+        try:
+            gdb.parse_and_eval('PyUnicodeUCS2_FromEncodedObject')
+        except RuntimeError:
+            return 'UCS4'
+        else:
+            return 'UCS2'
+    else:
+        return ''
+
+class PythonCodeExecutor(object):
+
+    Py_single_input = 256
+    Py_file_input = 257
+    Py_eval_input = 258
+
+    def malloc(self, size):
+        chunk = (gdb.parse_and_eval("(void *) malloc((size_t) %d)" % size))
+
+        pointer = pointervalue(chunk)
+        if pointer == 0:
+            raise gdb.GdbError("No memory could be allocated in the inferior.")
+
+        return pointer
+
+    def alloc_string(self, string):
+        pointer = self.malloc(len(string))
+        get_selected_inferior().write_memory(pointer, string)
+
+        return pointer
+
+    def alloc_pystring(self, string):
+        stringp = self.alloc_string(string)
+        PyString_FromStringAndSize = 'PyString_FromStringAndSize'
+
+        try:
+            gdb.parse_and_eval(PyString_FromStringAndSize)
+        except RuntimeError:
+            # Python 3
+            PyString_FromStringAndSize = ('PyUnicode%s_FromStringAndSize' %
+                                               (get_inferior_unicode_postfix(),))
+
+        try:
+            result = gdb.parse_and_eval(
+                '(PyObject *) %s((char *) %d, (size_t) %d)' % (
+                            PyString_FromStringAndSize, stringp, len(string)))
+        finally:
+            self.free(stringp)
+
+        pointer = pointervalue(result)
+        if pointer == 0:
+            raise gdb.GdbError("Unable to allocate Python string in "
+                               "the inferior.")
+
+        return pointer
+
+    def free(self, pointer):
+        gdb.parse_and_eval("free((void *) %d)" % pointer)
+
+    def incref(self, pointer):
+        "Increment the reference count of a Python object in the inferior."
+        gdb.parse_and_eval('Py_IncRef((PyObject *) %d)' % pointer)
+
+    def xdecref(self, pointer):
+        "Decrement the reference count of a Python object in the inferior."
+        # Py_DecRef is like Py_XDECREF, but a function. So we don't have
+        # to check for NULL. This should also decref all our allocated
+        # Python strings.
+        gdb.parse_and_eval('Py_DecRef((PyObject *) %d)' % pointer)
+
+    def evalcode(self, code, input_type, global_dict=None, local_dict=None):
+        """
+        Evaluate python code `code` given as a string in the inferior and
+        return the result as a gdb.Value. Returns a new reference in the
+        inferior.
+
+        Of course, executing any code in the inferior may be dangerous and may
+        leave the debuggee in an unsafe state or terminate it alltogether.
+        """
+        if '\0' in code:
+            raise gdb.GdbError("String contains NUL byte.")
+
+        code += '\0'
+
+        pointer = self.alloc_string(code)
+
+        globalsp = pointervalue(global_dict)
+        localsp = pointervalue(local_dict)
+
+        if globalsp == 0 or localsp == 0:
+            raise gdb.GdbError("Unable to obtain or create locals or globals.")
+
+        code = """
+            PyRun_String(
+                (char *) %(code)d,
+                (int) %(start)d,
+                (PyObject *) %(globals)s,
+                (PyObject *) %(locals)d)
+        """ % dict(code=pointer, start=input_type,
+                   globals=globalsp, locals=localsp)
+
+        with FetchAndRestoreError():
+            try:
+                pyobject_return_value = gdb.parse_and_eval(code)
+            finally:
+                self.free(pointer)
+
+        return pyobject_return_value
+
+class FetchAndRestoreError(PythonCodeExecutor):
+    """
+    Context manager that fetches the error indicator in the inferior and
+    restores it on exit.
+    """
+
+    def __init__(self):
+        self.sizeof_PyObjectPtr = gdb.lookup_type('PyObject').pointer().sizeof
+        self.pointer = self.malloc(self.sizeof_PyObjectPtr * 3)
+
+        type = self.pointer
+        value = self.pointer + self.sizeof_PyObjectPtr
+        traceback = self.pointer + self.sizeof_PyObjectPtr * 2
+
+        self.errstate = type, value, traceback
+
+    def __enter__(self):
+        gdb.parse_and_eval("PyErr_Fetch(%d, %d, %d)" % self.errstate)
+
+    def __exit__(self, *args):
+        if gdb.parse_and_eval("(int) PyErr_Occurred()"):
+            gdb.parse_and_eval("PyErr_Print()")
+
+        pyerr_restore = ("PyErr_Restore("
+                            "(PyObject *) *%d,"
+                            "(PyObject *) *%d,"
+                            "(PyObject *) *%d)")
+
+        try:
+            gdb.parse_and_eval(pyerr_restore % self.errstate)
+        finally:
+            self.free(self.pointer)
+
+
+class FixGdbCommand(gdb.Command):
+
+    def __init__(self, command, actual_command):
+        super(FixGdbCommand, self).__init__(command, gdb.COMMAND_DATA,
+                                            gdb.COMPLETE_NONE)
+        self.actual_command = actual_command
+
+    def fix_gdb(self):
+        """
+        It seems that invoking either 'cy exec' and 'py-exec' work perfectly 
+        fine, but after this gdb's python API is entirely broken. 
+        Maybe some uncleared exception value is still set?
+        sys.exc_clear() didn't help. A demonstration:
+
+        (gdb) cy exec 'hello'
+        'hello'
+        (gdb) python gdb.execute('cont')
+        RuntimeError: Cannot convert value to int.
+        Error while executing Python code.
+        (gdb) python gdb.execute('cont')
+        [15148 refs]
+
+        Program exited normally.
+        """
+        warnings.filterwarnings('ignore', r'.*', RuntimeWarning,
+                                re.escape(__name__))
+        try:
+            long(gdb.parse_and_eval("(void *) 0")) == 0
+        except RuntimeError:
+            pass
+        # warnings.resetwarnings()
+
+    def invoke(self, args, from_tty):
+        self.fix_gdb()
+        try:
+            gdb.execute('%s %s' % (self.actual_command, args))
+        except RuntimeError, e:
+            raise gdb.GdbError(str(e))
+        self.fix_gdb()
+
+
+def _evalcode_python(executor, code, input_type):
+    """
+    Execute Python code in the most recent stack frame.
+    """
+    global_dict = gdb.parse_and_eval('PyEval_GetGlobals()')
+    local_dict = gdb.parse_and_eval('PyEval_GetLocals()')
+
+    if (pointervalue(global_dict) == 0 or pointervalue(local_dict) == 0):
+        raise gdb.GdbError("Unable to find the locals or globals of the "
+                           "most recent Python function (relative to the "
+                           "selected frame).")
+
+    return executor.evalcode(code, input_type, global_dict, local_dict)
+
+class PyExec(gdb.Command):
+
+    def readcode(self, expr):
+        if expr:
+            return expr, PythonCodeExecutor.Py_single_input
+        else:
+            lines = []
+            while True:
+                try:
+                    line = raw_input('>')
+                except EOFError:
+                    break
+                else:
+                    if line.rstrip() == 'end':
+                        break
+
+                    lines.append(line)
+
+            return '\n'.join(lines), PythonCodeExecutor.Py_file_input
+
+    def invoke(self, expr, from_tty):
+        expr, input_type = self.readcode(expr)
+        executor = PythonCodeExecutor()
+        executor.xdecref(_evalcode_python(executor, input_type, global_dict,
+                                          local_dict))
+
+
+gdb.execute('set breakpoint pending on')
+
+if hasattr(gdb, 'GdbError'):
+     # Wrap py-step and py-next in gdb defines to make them repeatable.
+    py_step = PyStep('-py-step', PythonInfo())
+    py_next = PyNext('-py-next', PythonInfo())
+    register_defines()
+    py_finish = PyFinish('py-finish', PythonInfo())
+    py_run = PyRun('py-run', PythonInfo())
+    py_cont = PyCont('py-cont', PythonInfo())
+
+    py_exec = FixGdbCommand('py-exec', '-py-exec')
+    _py_exec = PyExec("-py-exec", gdb.COMMAND_DATA, gdb.COMPLETE_NONE)
+else:
+    warnings.warn("Use gdb 7.2 or higher to use the py-exec command.")