Add google-endpoints to third_party/.

third_party/google-endpoints/future/standard_library/__init__.py

+"""
+Python 3 reorganized the standard library (PEP 3108). This module exposes
+several standard library modules to Python 2 under their new Python 3
+names.
+
+It is designed to be used as follows::
+
+    from future import standard_library
+    standard_library.install_aliases()
+
+And then these normal Py3 imports work on both Py3 and Py2::
+
+    import builtins
+    import copyreg
+    import queue
+    import reprlib
+    import socketserver
+    import winreg    # on Windows only
+    import test.support
+    import html, html.parser, html.entites
+    import http, http.client, http.server
+    import http.cookies, http.cookiejar
+    import urllib.parse, urllib.request, urllib.response, urllib.error, urllib.robotparser
+    import xmlrpc.client, xmlrpc.server
+
+    import _thread
+    import _dummy_thread
+    import _markupbase
+
+    from itertools import filterfalse, zip_longest
+    from sys import intern
+    from collections import UserDict, UserList, UserString
+    from collections import OrderedDict, Counter     # even on Py2.6
+    from subprocess import getoutput, getstatusoutput
+    from subprocess import check_output              # even on Py2.6
+
+(The renamed modules and functions are still available under their old
+names on Python 2.)
+
+This is a cleaner alternative to this idiom (see
+http://docs.pythonsprints.com/python3_porting/py-porting.html)::
+
+    try:
+        import queue
+    except ImportError:
+        import Queue as queue
+
+
+Limitations
+-----------
+We don't currently support these modules, but would like to::
+
+    import dbm
+    import dbm.dumb
+    import dbm.gnu
+    import collections.abc  # on Py33
+    import pickle     # should (optionally) bring in cPickle on Python 2
+
+"""
+
+from __future__ import absolute_import, division, print_function
+
+import sys
+import logging
+import imp
+import contextlib
+import types
+import copy
+import os
+
+# Make a dedicated logger; leave the root logger to be configured
+# by the application.
+flog = logging.getLogger('future_stdlib')
+_formatter = logging.Formatter(logging.BASIC_FORMAT)
+_handler = logging.StreamHandler()
+_handler.setFormatter(_formatter)
+flog.addHandler(_handler)
+flog.setLevel(logging.WARN)
+
+from future.utils import PY2, PY3
+
+# The modules that are defined under the same names on Py3 but with
+# different contents in a significant way (e.g. submodules) are:
+#   pickle (fast one)
+#   dbm
+#   urllib
+#   test
+#   email
+
+REPLACED_MODULES = set(['test', 'urllib', 'pickle', 'dbm'])  # add email and dbm when we support it
+
+# The following module names are not present in Python 2.x, so they cause no
+# potential clashes between the old and new names:
+#   http
+#   html
+#   tkinter
+#   xmlrpc
+# Keys: Py2 / real module names
+# Values: Py3 / simulated module names
+RENAMES = {
+           # 'cStringIO': 'io',  # there's a new io module in Python 2.6
+                                 # that provides StringIO and BytesIO
+           # 'StringIO': 'io',   # ditto
+           # 'cPickle': 'pickle',
+           '__builtin__': 'builtins',
+           'copy_reg': 'copyreg',
+           'Queue': 'queue',
+           'future.moves.socketserver': 'socketserver',
+           'ConfigParser': 'configparser',
+           'repr': 'reprlib',
+           # 'FileDialog': 'tkinter.filedialog',
+           # 'tkFileDialog': 'tkinter.filedialog',
+           # 'SimpleDialog': 'tkinter.simpledialog',
+           # 'tkSimpleDialog': 'tkinter.simpledialog',
+           # 'tkColorChooser': 'tkinter.colorchooser',
+           # 'tkCommonDialog': 'tkinter.commondialog',
+           # 'Dialog': 'tkinter.dialog',
+           # 'Tkdnd': 'tkinter.dnd',
+           # 'tkFont': 'tkinter.font',
+           # 'tkMessageBox': 'tkinter.messagebox',
+           # 'ScrolledText': 'tkinter.scrolledtext',
+           # 'Tkconstants': 'tkinter.constants',
+           # 'Tix': 'tkinter.tix',
+           # 'ttk': 'tkinter.ttk',
+           # 'Tkinter': 'tkinter',
+           '_winreg': 'winreg',
+           'thread': '_thread',
+           'dummy_thread': '_dummy_thread',
+           # 'anydbm': 'dbm',   # causes infinite import loop
+           # 'whichdb': 'dbm',  # causes infinite import loop
+           # anydbm and whichdb are handled by fix_imports2
+           # 'dbhash': 'dbm.bsd',
+           # 'dumbdbm': 'dbm.dumb',
+           # 'dbm': 'dbm.ndbm',
+           # 'gdbm': 'dbm.gnu',
+           'future.moves.xmlrpc': 'xmlrpc',
+           # 'future.backports.email': 'email',    # for use by urllib
+           # 'DocXMLRPCServer': 'xmlrpc.server',
+           # 'SimpleXMLRPCServer': 'xmlrpc.server',
+           # 'httplib': 'http.client',
+           # 'htmlentitydefs' : 'html.entities',
+           # 'HTMLParser' : 'html.parser',
+           # 'Cookie': 'http.cookies',
+           # 'cookielib': 'http.cookiejar',
+           # 'BaseHTTPServer': 'http.server',
+           # 'SimpleHTTPServer': 'http.server',
+           # 'CGIHTTPServer': 'http.server',
+           # 'future.backports.test': 'test',  # primarily for renaming test_support to support
+           # 'commands': 'subprocess',
+           # 'urlparse' : 'urllib.parse',
+           # 'robotparser' : 'urllib.robotparser',
+           # 'abc': 'collections.abc',   # for Py33
+           # 'future.utils.six.moves.html': 'html',
+           # 'future.utils.six.moves.http': 'http',
+           'future.moves.html': 'html',
+           'future.moves.http': 'http',
+           # 'future.backports.urllib': 'urllib',
+           # 'future.utils.six.moves.urllib': 'urllib',
+           'future.moves._markupbase': '_markupbase',
+          }
+
+
+# It is complicated and apparently brittle to mess around with the
+# ``sys.modules`` cache in order to support "import urllib" meaning two
+# different things (Py2.7 urllib and backported Py3.3-like urllib) in different
+# contexts. So we require explicit imports for these modules.
+assert len(set(RENAMES.values()) & set(REPLACED_MODULES)) == 0
+
+
+# Harmless renames that we can insert.
+# These modules need names from elsewhere being added to them:
+#   subprocess: should provide getoutput and other fns from commands
+#               module but these fns are missing: getstatus, mk2arg,
+#               mkarg
+#   re:         needs an ASCII constant that works compatibly with Py3
+
+# etc: see lib2to3/fixes/fix_imports.py
+
+# (New module name, new object name, old module name, old object name)
+MOVES = [('collections', 'UserList', 'UserList', 'UserList'),
+         ('collections', 'UserDict', 'UserDict', 'UserDict'),
+         ('collections', 'UserString','UserString', 'UserString'),
+         ('itertools', 'filterfalse','itertools', 'ifilterfalse'),
+         ('itertools', 'zip_longest','itertools', 'izip_longest'),
+         ('sys', 'intern','__builtin__', 'intern'),
+         # The re module has no ASCII flag in Py2, but this is the default.
+         # Set re.ASCII to a zero constant. stat.ST_MODE just happens to be one
+         # (and it exists on Py2.6+).
+         ('re', 'ASCII','stat', 'ST_MODE'),
+         ('base64', 'encodebytes','base64', 'encodestring'),
+         ('base64', 'decodebytes','base64', 'decodestring'),
+         ('subprocess', 'getoutput', 'commands', 'getoutput'),
+         ('subprocess', 'getstatusoutput', 'commands', 'getstatusoutput'),
+         ('subprocess', 'check_output', 'future.backports.misc', 'check_output'),
+         ('math', 'ceil', 'future.backports.misc', 'ceil'),
+         ('collections', 'OrderedDict', 'future.backports.misc', 'OrderedDict'),
+         ('collections', 'Counter', 'future.backports.misc', 'Counter'),
+         ('itertools', 'count', 'future.backports.misc', 'count'),
+         ('reprlib', 'recursive_repr', 'future.backports.misc', 'recursive_repr'),
+         ('functools', 'cmp_to_key', 'future.backports.misc', 'cmp_to_key'),
+
+# This is no use, since "import urllib.request" etc. still fails:
+#          ('urllib', 'error', 'future.moves.urllib', 'error'),
+#          ('urllib', 'parse', 'future.moves.urllib', 'parse'),
+#          ('urllib', 'request', 'future.moves.urllib', 'request'),
+#          ('urllib', 'response', 'future.moves.urllib', 'response'),
+#          ('urllib', 'robotparser', 'future.moves.urllib', 'robotparser'),
+        ]
+
+
+# A minimal example of an import hook:
+# class WarnOnImport(object):
+#     def __init__(self, *args):
+#         self.module_names = args
+#
+#     def find_module(self, fullname, path=None):
+#         if fullname in self.module_names:
+#             self.path = path
+#             return self
+#         return None
+#
+#     def load_module(self, name):
+#         if name in sys.modules:
+#             return sys.modules[name]
+#         module_info = imp.find_module(name, self.path)
+#         module = imp.load_module(name, *module_info)
+#         sys.modules[name] = module
+#         flog.warning("Imported deprecated module %s", name)
+#         return module
+
+
+class RenameImport(object):
+    """
+    A class for import hooks mapping Py3 module names etc. to the Py2 equivalents.
+    """
+    # Different RenameImport classes are created when importing this module from
+    # different source files. This causes isinstance(hook, RenameImport) checks
+    # to produce inconsistent results. We add this RENAMER attribute here so
+    # remove_hooks() and install_hooks() can find instances of these classes
+    # easily:
+    RENAMER = True
+
+    def __init__(self, old_to_new):
+        '''
+        Pass in a dictionary-like object mapping from old names to new
+        names. E.g. {'ConfigParser': 'configparser', 'cPickle': 'pickle'}
+        '''
+        self.old_to_new = old_to_new
+        both = set(old_to_new.keys()) & set(old_to_new.values())
+        assert (len(both) == 0 and
+                len(set(old_to_new.values())) == len(old_to_new.values())), \
+               'Ambiguity in renaming (handler not implemented)'
+        self.new_to_old = dict((new, old) for (old, new) in old_to_new.items())
+
+    def find_module(self, fullname, path=None):
+        # Handles hierarchical importing: package.module.module2
+        new_base_names = set([s.split('.')[0] for s in self.new_to_old])
+        # Before v0.12: Was: if fullname in set(self.old_to_new) | new_base_names:
+        if fullname in new_base_names:
+            return self
+        return None
+
+    def load_module(self, name):
+        path = None
+        if name in sys.modules:
+            return sys.modules[name]
+        elif name in self.new_to_old:
+            # New name. Look up the corresponding old (Py2) name:
+            oldname = self.new_to_old[name]
+            module = self._find_and_load_module(oldname)
+            # module.__future_module__ = True
+        else:
+            module = self._find_and_load_module(name)
+        # In any case, make it available under the requested (Py3) name
+        sys.modules[name] = module
+        return module
+
+    def _find_and_load_module(self, name, path=None):
+        """
+        Finds and loads it. But if there's a . in the name, handles it
+        properly.
+        """
+        bits = name.split('.')
+        while len(bits) > 1:
+            # Treat the first bit as a package
+            packagename = bits.pop(0)
+            package = self._find_and_load_module(packagename, path)
+            try:
+                path = package.__path__
+            except AttributeError:
+                # This could be e.g. moves.
+                flog.debug('Package {0} has no __path__.'.format(package))
+                if name in sys.modules:
+                    return sys.modules[name]
+                flog.debug('What to do here?')
+
+        name = bits[0]
+        module_info = imp.find_module(name, path)
+        return imp.load_module(name, *module_info)
+
+
+class hooks(object):
+    """
+    Acts as a context manager. Saves the state of sys.modules and restores it
+    after the 'with' block.
+
+    Use like this:
+
+    >>> from future import standard_library
+    >>> with standard_library.hooks():
+    ...     import http.client
+    >>> import requests
+
+    For this to work, http.client will be scrubbed from sys.modules after the
+    'with' block. That way the modules imported in the 'with' block will
+    continue to be accessible in the current namespace but not from any
+    imported modules (like requests).
+    """
+    def __enter__(self):
+        # flog.debug('Entering hooks context manager')
+        self.old_sys_modules = copy.copy(sys.modules)
+        self.hooks_were_installed = detect_hooks()
+        # self.scrubbed = scrub_py2_sys_modules()
+        install_hooks()
+        return self
+
+    def __exit__(self, *args):
+        # flog.debug('Exiting hooks context manager')
+        # restore_sys_modules(self.scrubbed)
+        if not self.hooks_were_installed:
+            remove_hooks()
+        # scrub_future_sys_modules()
+
+# Sanity check for is_py2_stdlib_module(): We aren't replacing any
+# builtin modules names:
+if PY2:
+    assert len(set(RENAMES.values()) & set(sys.builtin_module_names)) == 0
+
+
+def is_py2_stdlib_module(m):
+    """
+    Tries to infer whether the module m is from the Python 2 standard library.
+    This may not be reliable on all systems.
+    """
+    if PY3:
+        return False
+    if not 'stdlib_path' in is_py2_stdlib_module.__dict__:
+        stdlib_files = [contextlib.__file__, os.__file__, copy.__file__]
+        stdlib_paths = [os.path.split(f)[0] for f in stdlib_files]
+        if not len(set(stdlib_paths)) == 1:
+            # This seems to happen on travis-ci.org. Very strange. We'll try to
+            # ignore it.
+            flog.warn('Multiple locations found for the Python standard '
+                         'library: %s' % stdlib_paths)
+        # Choose the first one arbitrarily
+        is_py2_stdlib_module.stdlib_path = stdlib_paths[0]
+
+    if m.__name__ in sys.builtin_module_names:
+        return True
+
+    if hasattr(m, '__file__'):
+        modpath = os.path.split(m.__file__)
+        if (modpath[0].startswith(is_py2_stdlib_module.stdlib_path) and
+            'site-packages' not in modpath[0]):
+            return True
+
+    return False
+
+
+def scrub_py2_sys_modules():
+    """
+    Removes any Python 2 standard library modules from ``sys.modules`` that
+    would interfere with Py3-style imports using import hooks. Examples are
+    modules with the same names (like urllib or email).
+
+    (Note that currently import hooks are disabled for modules like these
+    with ambiguous names anyway ...)
+    """
+    if PY3:
+        return {}
+    scrubbed = {}
+    for modulename in REPLACED_MODULES & set(RENAMES.keys()):
+        if not modulename in sys.modules:
+            continue
+
+        module = sys.modules[modulename]
+
+        if is_py2_stdlib_module(module):
+            flog.debug('Deleting (Py2) {} from sys.modules'.format(modulename))
+            scrubbed[modulename] = sys.modules[modulename]
+            del sys.modules[modulename]
+    return scrubbed
+
+
+def scrub_future_sys_modules():
+    """
+    Deprecated.
+    """
+    return {}    
+
+class suspend_hooks(object):
+    """
+    Acts as a context manager. Use like this:
+
+    >>> from future import standard_library
+    >>> standard_library.install_hooks()
+    >>> import http.client
+    >>> # ...
+    >>> with standard_library.suspend_hooks():
+    >>>     import requests     # incompatible with ``future``'s standard library hooks
+
+    If the hooks were disabled before the context, they are not installed when
+    the context is left.
+    """
+    def __enter__(self):
+        self.hooks_were_installed = detect_hooks()
+        remove_hooks()
+        # self.scrubbed = scrub_future_sys_modules()
+        return self
+
+    def __exit__(self, *args):
+        if self.hooks_were_installed:
+            install_hooks()
+        # restore_sys_modules(self.scrubbed)
+
+
+def restore_sys_modules(scrubbed):
+    """
+    Add any previously scrubbed modules back to the sys.modules cache,
+    but only if it's safe to do so.
+    """
+    clash = set(sys.modules) & set(scrubbed)
+    if len(clash) != 0:
+        # If several, choose one arbitrarily to raise an exception about
+        first = list(clash)[0]
+        raise ImportError('future module {} clashes with Py2 module'
+                          .format(first))
+    sys.modules.update(scrubbed)
+
+
+def install_aliases():
+    """
+    Monkey-patches the standard library in Py2.6/7 to provide
+    aliases for better Py3 compatibility.
+    """
+    if PY3:
+        return
+    # if hasattr(install_aliases, 'run_already'):
+    #     return
+    for (newmodname, newobjname, oldmodname, oldobjname) in MOVES:
+        __import__(newmodname)
+        # We look up the module in sys.modules because __import__ just returns the
+        # top-level package:
+        newmod = sys.modules[newmodname]
+        # newmod.__future_module__ = True
+
+        __import__(oldmodname)
+        oldmod = sys.modules[oldmodname]
+
+        obj = getattr(oldmod, oldobjname)
+        setattr(newmod, newobjname, obj)
+
+    # Hack for urllib so it appears to have the same structure on Py2 as on Py3
+    import urllib
+    from future.backports.urllib import request
+    from future.backports.urllib import response
+    from future.backports.urllib import parse
+    from future.backports.urllib import error
+    from future.backports.urllib import robotparser
+    urllib.request = request
+    urllib.response = response
+    urllib.parse = parse
+    urllib.error = error
+    urllib.robotparser = robotparser
+    sys.modules['urllib.request'] = request
+    sys.modules['urllib.response'] = response
+    sys.modules['urllib.parse'] = parse
+    sys.modules['urllib.error'] = error
+    sys.modules['urllib.robotparser'] = robotparser
+
+    # Patch the test module so it appears to have the same structure on Py2 as on Py3
+    try:
+        import test
+    except ImportError:
+        pass
+    try:
+        from future.moves.test import support
+    except ImportError:
+        pass
+    else:
+        test.support = support
+        sys.modules['test.support'] = support
+
+    # Patch the dbm module so it appears to have the same structure on Py2 as on Py3
+    try:
+        import dbm
+    except ImportError:
+        pass
+    else:
+        from future.moves.dbm import dumb
+        dbm.dumb = dumb
+        sys.modules['dbm.dumb'] = dumb
+        try:
+            from future.moves.dbm import gnu
+        except ImportError:
+            pass
+        else:
+            dbm.gnu = gnu
+            sys.modules['dbm.gnu'] = gnu
+        try:
+            from future.moves.dbm import ndbm
+        except ImportError:
+            pass
+        else:
+            dbm.ndbm = ndbm
+            sys.modules['dbm.ndbm'] = ndbm
+
+    # install_aliases.run_already = True
+
+
+def install_hooks():
+    """
+    This function installs the future.standard_library import hook into
+    sys.meta_path.
+    """
+    if PY3:
+        return
+
+    install_aliases()
+
+    flog.debug('sys.meta_path was: {0}'.format(sys.meta_path))
+    flog.debug('Installing hooks ...')
+
+    # Add it unless it's there already
+    newhook = RenameImport(RENAMES)
+    if not detect_hooks():
+        sys.meta_path.append(newhook)
+    flog.debug('sys.meta_path is now: {0}'.format(sys.meta_path))
+
+
+def enable_hooks():
+    """
+    Deprecated. Use install_hooks() instead. This will be removed by
+    ``future`` v1.0.
+    """
+    install_hooks()
+
+
+def remove_hooks(scrub_sys_modules=False):
+    """
+    This function removes the import hook from sys.meta_path.
+    """
+    if PY3:
+        return
+    flog.debug('Uninstalling hooks ...')
+    # Loop backwards, so deleting items keeps the ordering:
+    for i, hook in list(enumerate(sys.meta_path))[::-1]:
+        if hasattr(hook, 'RENAMER'):
+            del sys.meta_path[i]
+
+    # Explicit is better than implicit. In the future the interface should
+    # probably change so that scrubbing the import hooks requires a separate
+    # function call. Left as is for now for backward compatibility with
+    # v0.11.x.
+    if scrub_sys_modules:
+        scrub_future_sys_modules()
+
+
+def disable_hooks():
+    """
+    Deprecated. Use remove_hooks() instead. This will be removed by
+    ``future`` v1.0.
+    """
+    remove_hooks()
+
+
+def detect_hooks():
+    """
+    Returns True if the import hooks are installed, False if not.
+    """
+    flog.debug('Detecting hooks ...')
+    present = any([hasattr(hook, 'RENAMER') for hook in sys.meta_path])
+    if present:
+        flog.debug('Detected.')
+    else:
+        flog.debug('Not detected.')
+    return present
+
+
+# As of v0.12, this no longer happens implicitly:
+# if not PY3:
+#     install_hooks()
+
+
+if not hasattr(sys, 'py2_modules'):
+    sys.py2_modules = {}
+
+def cache_py2_modules():
+    """
+    Currently this function is unneeded, as we are not attempting to provide import hooks
+    for modules with ambiguous names: email, urllib, pickle.
+    """
+    if len(sys.py2_modules) != 0:
+        return
+    assert not detect_hooks()
+    import urllib
+    sys.py2_modules['urllib'] = urllib
+
+    import email
+    sys.py2_modules['email'] = email
+
+    import pickle
+    sys.py2_modules['pickle'] = pickle
+
+    # Not all Python installations have test module. (Anaconda doesn't, for example.)
+    # try:
+    #     import test
+    # except ImportError:
+    #     sys.py2_modules['test'] = None
+    # sys.py2_modules['test'] = test
+
+    # import dbm
+    # sys.py2_modules['dbm'] = dbm
+
+
+def import_(module_name, backport=False):
+    """
+    Pass a (potentially dotted) module name of a Python 3 standard library
+    module. This function imports the module compatibly on Py2 and Py3 and
+    returns the top-level module.
+
+    Example use:
+        >>> http = import_('http.client')
+        >>> http = import_('http.server')
+        >>> urllib = import_('urllib.request')
+
+    Then:
+        >>> conn = http.client.HTTPConnection(...)
+        >>> response = urllib.request.urlopen('http://mywebsite.com')
+        >>> # etc.
+
+    Use as follows:
+        >>> package_name = import_(module_name)
+
+    On Py3, equivalent to this:
+
+        >>> import module_name
+
+    On Py2, equivalent to this if backport=False:
+
+        >>> from future.moves import module_name
+
+    or to this if backport=True:
+
+        >>> from future.backports import module_name
+
+    except that it also handles dotted module names such as ``http.client``
+    The effect then is like this:
+
+        >>> from future.backports import module
+        >>> from future.backports.module import submodule
+        >>> module.submodule = submodule
+
+    Note that this would be a SyntaxError in Python:
+
+        >>> from future.backports import http.client
+
+    """
+    # Python 2.6 doesn't have importlib in the stdlib, so it requires
+    # the backported ``importlib`` package from PyPI as a dependency to use
+    # this function:
+    import importlib
+
+    if PY3:
+        return __import__(module_name)
+    else:
+        # client.blah = blah
+        # Then http.client = client
+        # etc.
+        if backport:
+            prefix = 'future.backports'
+        else:
+            prefix = 'future.moves'
+        parts = prefix.split('.') + module_name.split('.')
+
+        modules = []
+        for i, part in enumerate(parts):
+            sofar = '.'.join(parts[:i+1])
+            modules.append(importlib.import_module(sofar))
+        for i, part in reversed(list(enumerate(parts))):
+            if i == 0:
+                break
+            setattr(modules[i-1], part, modules[i])
+
+        # Return the next-most top-level module after future.backports / future.moves:
+        return modules[2]
+
+
+def from_import(module_name, *symbol_names, **kwargs):
+    """
+    Example use:
+        >>> HTTPConnection = from_import('http.client', 'HTTPConnection')
+        >>> HTTPServer = from_import('http.server', 'HTTPServer')
+        >>> urlopen, urlparse = from_import('urllib.request', 'urlopen', 'urlparse')
+
+    Equivalent to this on Py3:
+
+        >>> from module_name import symbol_names[0], symbol_names[1], ...
+
+    and this on Py2:
+
+        >>> from future.moves.module_name import symbol_names[0], ...
+
+    or:
+
+        >>> from future.backports.module_name import symbol_names[0], ...
+
+    except that it also handles dotted module names such as ``http.client``.
+    """
+
+    if PY3:
+        return __import__(module_name)
+    else:
+        if 'backport' in kwargs and bool(kwargs['backport']):
+            prefix = 'future.backports'
+        else:
+            prefix = 'future.moves'
+        parts = prefix.split('.') + module_name.split('.')
+        module = importlib.import_module(prefix + '.' + module_name)
+        output = [getattr(module, name) for name in symbol_names]
+        if len(output) == 1:
+            return output[0]
+        else:
+            return output
+
+
+class exclude_local_folder_imports(object):
+    """
+    A context-manager that prevents standard library modules like configparser
+    from being imported from the local python-future source folder on Py3.
+
+    (This was need prior to v0.16.0 because the presence of a configparser
+    folder would otherwise have prevented setuptools from running on Py3. Maybe
+    it's not needed any more?)
+    """
+    def __init__(self, *args):
+        assert len(args) > 0
+        self.module_names = args
+        # Disallow dotted module names like http.client:
+        if any(['.' in m for m in self.module_names]):
+            raise NotImplementedError('Dotted module names are not supported')
+
+    def __enter__(self):
+        self.old_sys_path = copy.copy(sys.path)
+        self.old_sys_modules = copy.copy(sys.modules)
+        if sys.version_info[0] < 3:
+            return
+        # The presence of all these indicates we've found our source folder,
+        # because `builtins` won't have been installed in site-packages by setup.py:
+        FUTURE_SOURCE_SUBFOLDERS = ['future', 'past', 'libfuturize', 'libpasteurize', 'builtins']
+
+        # Look for the future source folder:
+        for folder in self.old_sys_path:
+            if all([os.path.exists(os.path.join(folder, subfolder))
+                    for subfolder in FUTURE_SOURCE_SUBFOLDERS]):
+                # Found it. Remove it.
+                sys.path.remove(folder)
+
+        # Ensure we import the system module:
+        for m in self.module_names:
+            # Delete the module and any submodules from sys.modules:
+            # for key in list(sys.modules):
+            #     if key == m or key.startswith(m + '.'):
+            #         try:
+            #             del sys.modules[key]
+            #         except KeyError:
+            #             pass
+            try:
+                module = __import__(m, level=0)
+            except ImportError:
+                # There's a problem importing the system module. E.g. the
+                # winreg module is not available except on Windows.
+                pass
+
+    def __exit__(self, *args):
+        # Restore sys.path and sys.modules:
+        sys.path = self.old_sys_path
+        for m in set(self.old_sys_modules.keys()) - set(sys.modules.keys()):
+            sys.modules[m] = self.old_sys_modules[m]
+
+TOP_LEVEL_MODULES = ['builtins',
+                     'copyreg',
+                     'html',
+                     'http',
+                     'queue',
+                     'reprlib',
+                     'socketserver',
+                     'test',
+                     'tkinter',
+                     'winreg',
+                     'xmlrpc',
+                     '_dummy_thread',
+                     '_markupbase',
+                     '_thread',
+                    ]
+
+def import_top_level_modules():
+    with exclude_local_folder_imports(*TOP_LEVEL_MODULES):
+        for m in TOP_LEVEL_MODULES:
+            try:
+                __import__(m)
+            except ImportError:     # e.g. winreg
+                pass