[Telemetry] Add pyfakefs to telemetry/third_party

tools/telemetry/third_party/pyfakefs/pyfakefs/fake_filesystem.py

+# Copyright 2009 Google Inc. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# pylint: disable-msg=W0612,W0613,C6409
+
+"""A fake filesystem implementation for unit testing.
+
+Includes:
+  FakeFile:  Provides the appearance of a real file.
+  FakeDirectory: Provides the appearance of a real dir.
+  FakeFilesystem:  Provides the appearance of a real directory hierarchy.
+  FakeOsModule:  Uses FakeFilesystem to provide a fake os module replacement.
+  FakePathModule:  Faked os.path module replacement.
+  FakeFileOpen:  Faked file() and open() function replacements.
+
+Usage:
+>>> import fake_filesystem
+>>> filesystem = fake_filesystem.FakeFilesystem()
+>>> os_module = fake_filesystem.FakeOsModule(filesystem)
+>>> pathname = '/a/new/dir/new-file'
+
+Create a new file object, creating parent directory objects as needed:
+>>> os_module.path.exists(pathname)
+False
+>>> new_file = filesystem.CreateFile(pathname)
+
+File objects can't be overwritten:
+>>> os_module.path.exists(pathname)
+True
+>>> try:
+...   filesystem.CreateFile(pathname)
+... except IOError as e:
+...   assert e.errno == errno.EEXIST, 'unexpected errno: %d' % e.errno
+...   assert e.strerror == 'File already exists in fake filesystem'
+
+Remove a file object:
+>>> filesystem.RemoveObject(pathname)
+>>> os_module.path.exists(pathname)
+False
+
+Create a new file object at the previous path:
+>>> beatles_file = filesystem.CreateFile(pathname,
+...     contents='Dear Prudence\\nWon\\'t you come out to play?\\n')
+>>> os_module.path.exists(pathname)
+True
+
+Use the FakeFileOpen class to read fake file objects:
+>>> file_module = fake_filesystem.FakeFileOpen(filesystem)
+>>> for line in file_module(pathname):
+...     print line.rstrip()
+...
+Dear Prudence
+Won't you come out to play?
+
+File objects cannot be treated like directory objects:
+>>> os_module.listdir(pathname)  #doctest: +NORMALIZE_WHITESPACE
+Traceback (most recent call last):
+  File "fake_filesystem.py", line 291, in listdir
+    raise OSError(errno.ENOTDIR,
+OSError: [Errno 20] Fake os module: not a directory: '/a/new/dir/new-file'
+
+The FakeOsModule can list fake directory objects:
+>>> os_module.listdir(os_module.path.dirname(pathname))
+['new-file']
+
+The FakeOsModule also supports stat operations:
+>>> import stat
+>>> stat.S_ISREG(os_module.stat(pathname).st_mode)
+True
+>>> stat.S_ISDIR(os_module.stat(os_module.path.dirname(pathname)).st_mode)
+True
+"""
+
+import errno
+import heapq
+import os
+import stat
+import sys
+import time
+import warnings
+try:
+  import cStringIO as io  # pylint: disable-msg=C6204
+except ImportError:
+  import io  # pylint: disable-msg=C6204
+
+__pychecker__ = 'no-reimportself'
+
+__version__ = '2.5'
+
+PERM_READ = 0o400      # Read permission bit.
+PERM_WRITE = 0o200     # Write permission bit.
+PERM_EXE = 0o100       # Write permission bit.
+PERM_DEF = 0o777       # Default permission bits.
+PERM_DEF_FILE = 0o666  # Default permission bits (regular file)
+PERM_ALL = 0o7777      # All permission bits.
+
+_OPEN_MODE_MAP = {
+    # mode name:(file must exist, need read, need write,
+    #            truncate [implies need write], append)
+    'r': (True, True, False, False, False),
+    'w': (False, False, True, True, False),
+    'a': (False, False, True, False, True),
+    'r+': (True, True, True, False, False),
+    'w+': (False, True, True, True, False),
+    'a+': (False, True, True, False, True),
+    }
+
+_MAX_LINK_DEPTH = 20
+
+FAKE_PATH_MODULE_DEPRECATION = ('Do not instantiate a FakePathModule directly; '
+                                'let FakeOsModule instantiate it.  See the '
+                                'FakeOsModule docstring for details.')
+
+
+class Error(Exception):
+  pass
+
+_is_windows = sys.platform.startswith('win')
+_is_cygwin = sys.platform == 'cygwin'
+
+if _is_windows:
+  # On Windows, raise WindowsError instead of OSError if available
+  OSError = WindowsError  # pylint: disable-msg=E0602,W0622
+
+
+class FakeLargeFileIoException(Error):
+  def __init__(self, file_path):
+    Error.__init__(self,
+                   'Read and write operations not supported for '
+                   'fake large file: %s' % file_path)
+
+
+def CopyModule(old):
+  """Recompiles and creates new module object."""
+  saved = sys.modules.pop(old.__name__, None)
+  new = __import__(old.__name__)
+  sys.modules[old.__name__] = saved
+  return new
+
+
+class FakeFile(object):
+  """Provides the appearance of a real file.
+
+     Attributes currently faked out:
+       st_mode: user-specified, otherwise S_IFREG
+       st_ctime: the time.time() timestamp when the file is created.
+       st_size: the size of the file
+
+     Other attributes needed by os.stat are assigned default value of None
+      these include: st_ino, st_dev, st_nlink, st_uid, st_gid, st_atime,
+      st_mtime
+  """
+
+  def __init__(self, name, st_mode=stat.S_IFREG | PERM_DEF_FILE,
+               contents=None):
+    """init.
+
+    Args:
+      name:  name of the file/directory, without parent path information
+      st_mode:  the stat.S_IF* constant representing the file type (i.e.
+        stat.S_IFREG, stat.SIFDIR)
+      contents:  the contents of the filesystem object; should be a string for
+        regular files, and a list of other FakeFile or FakeDirectory objects
+        for FakeDirectory objects
+    """
+    self.name = name
+    self.st_mode = st_mode
+    self.contents = contents
+    self.epoch = 0
+    self.st_ctime = int(time.time())
+    self.st_atime = self.st_ctime
+    self.st_mtime = self.st_ctime
+    if contents:
+      self.st_size = len(contents)
+    else:
+      self.st_size = 0
+    # Non faked features, write setter methods for fakeing them
+    self.st_ino = None
+    self.st_dev = None
+    self.st_nlink = None
+    self.st_uid = None
+    self.st_gid = None
+
+  def SetLargeFileSize(self, st_size):
+    """Sets the self.st_size attribute and replaces self.content with None.
+
+    Provided specifically to simulate very large files without regards
+    to their content (which wouldn't fit in memory)
+
+    Args:
+      st_size: The desired file size
+
+    Raises:
+      IOError: if the st_size is not a non-negative integer
+    """
+    # the st_size should be an positive integer value
+    if not isinstance(st_size, int) or st_size < 0:
+      raise IOError(errno.ENOSPC,
+                    'Fake file object: can not create non negative integer '
+                    'size=%r fake file' % st_size,
+                    self.name)
+
+    self.st_size = st_size
+    self.contents = None
+
+  def IsLargeFile(self):
+    """Return True if this file was initialized with size but no contents."""
+    return self.contents is None
+
+  def SetContents(self, contents):
+    """Sets the file contents and size.
+
+    Args:
+      contents: string, new content of file.
+    """
+    # convert a byte array to a string
+    if sys.version_info >= (3, 0) and isinstance(contents, bytes):
+      contents = ''.join(chr(i) for i in contents)
+    self.contents = contents
+    self.st_size = len(contents)
+    self.epoch += 1
+
+  def SetSize(self, st_size):
+    """Resizes file content, padding with nulls if new size exceeds the old.
+
+    Args:
+      st_size: The desired size for the file.
+
+    Raises:
+      IOError: if the st_size arg is not a non-negative integer
+    """
+
+    if not isinstance(st_size, int) or st_size < 0:
+      raise IOError(errno.ENOSPC,
+                    'Fake file object: can not create non negative integer '
+                    'size=%r fake file' % st_size,
+                    self.name)
+
+    current_size = len(self.contents)
+    if st_size < current_size:
+      self.contents = self.contents[:st_size]
+    else:
+      self.contents = '%s%s' % (self.contents, '\0' * (st_size - current_size))
+    self.st_size = len(self.contents)
+    self.epoch += 1
+
+  def SetATime(self, st_atime):
+    """Set the self.st_atime attribute.
+
+    Args:
+      st_atime: The desired atime.
+    """
+    self.st_atime = st_atime
+
+  def SetMTime(self, st_mtime):
+    """Set the self.st_mtime attribute.
+
+    Args:
+      st_mtime: The desired mtime.
+    """
+    self.st_mtime = st_mtime
+
+  def __str__(self):
+    return '%s(%o)' % (self.name, self.st_mode)
+
+  def SetIno(self, st_ino):
+    """Set the self.st_ino attribute.
+
+    Args:
+      st_ino: The desired inode.
+    """
+    self.st_ino = st_ino
+
+
+class FakeDirectory(FakeFile):
+  """Provides the appearance of a real dir."""
+
+  def __init__(self, name, perm_bits=PERM_DEF):
+    """init.
+
+    Args:
+      name:  name of the file/directory, without parent path information
+      perm_bits: permission bits. defaults to 0o777.
+    """
+    FakeFile.__init__(self, name, stat.S_IFDIR | perm_bits, {})
+
+  def AddEntry(self, pathname):
+    """Adds a child FakeFile to this directory.
+
+    Args:
+      pathname:  FakeFile instance to add as a child of this directory
+    """
+    self.contents[pathname.name] = pathname
+
+  def GetEntry(self, pathname_name):
+    """Retrieves the specified child file or directory.
+
+    Args:
+      pathname_name: basename of the child object to retrieve
+    Returns:
+      string, file contents
+    Raises:
+      KeyError: if no child exists by the specified name
+    """
+    return self.contents[pathname_name]
+
+  def RemoveEntry(self, pathname_name):
+    """Removes the specified child file or directory.
+
+    Args:
+      pathname_name: basename of the child object to remove
+
+    Raises:
+      KeyError: if no child exists by the specified name
+    """
+    del self.contents[pathname_name]
+
+  def __str__(self):
+    rc = super(FakeDirectory, self).__str__() + ':\n'
+    for item in self.contents:
+      item_desc = self.contents[item].__str__()
+      for line in item_desc.split('\n'):
+        if line:
+          rc = rc + '  ' + line + '\n'
+    return rc
+
+
+class FakeFilesystem(object):
+  """Provides the appearance of a real directory tree for unit testing."""
+
+  def __init__(self, path_separator=os.path.sep):
+    """init.
+
+    Args:
+      path_separator:  optional substitute for os.path.sep
+    """
+    self.path_separator = path_separator
+    self.root = FakeDirectory(self.path_separator)
+    self.cwd = self.root.name
+    # We can't query the current value without changing it:
+    self.umask = os.umask(0o22)
+    os.umask(self.umask)
+    # A list of open file objects. Their position in the list is their
+    # file descriptor number
+    self.open_files = []
+    # A heap containing all free positions in self.open_files list
+    self.free_fd_heap = []
+
+  def SetIno(self, path, st_ino):
+    """Set the self.st_ino attribute of file at 'path'.
+
+    Args:
+      path: Path to file.
+      st_ino: The desired inode.
+    """
+    self.GetObject(path).SetIno(st_ino)
+
+  def AddOpenFile(self, file_obj):
+    """Adds file_obj to the list of open files on the filesystem.
+
+    The position in the self.open_files array is the file descriptor number
+
+    Args:
+      file_obj:  file object to be added to open files list.
+
+    Returns:
+      File descriptor number for the file object.
+    """
+    if self.free_fd_heap:
+      open_fd = heapq.heappop(self.free_fd_heap)
+      self.open_files[open_fd] = file_obj
+      return open_fd
+
+    self.open_files.append(file_obj)
+    return len(self.open_files) - 1
+
+  def CloseOpenFile(self, file_obj):
+    """Removes file_obj from the list of open files on the filesystem.
+
+    Sets the entry in open_files to None.
+
+    Args:
+      file_obj:  file object to be removed to open files list.
+    """
+    self.open_files[file_obj.filedes] = None
+    heapq.heappush(self.free_fd_heap, file_obj.filedes)
+
+  def GetOpenFile(self, file_des):
+    """Returns an open file.
+
+    Args:
+      file_des:  file descriptor of the open file.
+
+    Raises:
+      OSError: an invalid file descriptor.
+      TypeError: filedes is not an integer.
+
+    Returns:
+      Open file object.
+    """
+    if not isinstance(file_des, int):
+      raise TypeError('an integer is required')
+    if (file_des >= len(self.open_files) or
+        self.open_files[file_des] is None):
+      raise OSError(errno.EBADF, 'Bad file descriptor', file_des)
+    return self.open_files[file_des]
+
+  def CollapsePath(self, path):
+    """Mimics os.path.normpath using the specified path_separator.
+
+    Mimics os.path.normpath using the path_separator that was specified
+    for this FakeFilesystem.  Normalizes the path, but unlike the method
+    NormalizePath, does not make it absolute.  Eliminates dot components
+    (. and ..) and combines repeated path separators (//).  Initial ..
+    components are left in place for relative paths.  If the result is an empty
+    path, '.' is returned instead.  Unlike the real os.path.normpath, this does
+    not replace '/' with '\\' on Windows.
+
+    Args:
+      path:  (str) The path to normalize.
+
+    Returns:
+      (str) A copy of path with empty components and dot components removed.
+    """
+    is_absolute_path = path.startswith(self.path_separator)
+    path_components = path.split(self.path_separator)
+    collapsed_path_components = []
+    for component in path_components:
+      if (not component) or (component == '.'):
+        continue
+      if component == '..':
+        if collapsed_path_components and (
+            collapsed_path_components[-1] != '..'):
+          # Remove an up-reference: directory/..
+          collapsed_path_components.pop()
+          continue
+        elif is_absolute_path:
+          # Ignore leading .. components if starting from the root directory.
+          continue
+      collapsed_path_components.append(component)
+    collapsed_path = self.path_separator.join(collapsed_path_components)
+    if is_absolute_path:
+      collapsed_path = self.path_separator + collapsed_path
+    return collapsed_path or '.'
+
+  def NormalizePath(self, path):
+    """Absolutize and minimalize the given path.
+
+    Forces all relative paths to be absolute, and normalizes the path to
+    eliminate dot and empty components.
+
+    Args:
+      path:  path to normalize
+
+    Returns:
+      The normalized path relative to the current working directory, or the root
+        directory if path is empty.
+    """
+    if not path:
+      path = self.path_separator
+    elif not path.startswith(self.path_separator):
+      # Prefix relative paths with cwd, if cwd is not root.
+      path = self.path_separator.join(
+          (self.cwd != self.root.name and self.cwd or '',
+           path))
+    if path == '.':
+      path = self.cwd
+    return self.CollapsePath(path)
+
+  def SplitPath(self, path):
+    """Mimics os.path.split using the specified path_separator.
+
+    Mimics os.path.split using the path_separator that was specified
+    for this FakeFilesystem.
+
+    Args:
+      path:  (str) The path to split.
+
+    Returns:
+      (str) A duple (pathname, basename) for which pathname does not
+          end with a slash, and basename does not contain a slash.
+    """
+    path_components = path.split(self.path_separator)
+    if not path_components:
+      return ('', '')
+    basename = path_components.pop()
+    if not path_components:
+      return ('', basename)
+    for component in path_components:
+      if component:
+        # The path is not the root; it contains a non-separator component.
+        # Strip all trailing separators.
+        while not path_components[-1]:
+          path_components.pop()
+        return (self.path_separator.join(path_components), basename)
+    # Root path.  Collapse all leading separators.
+    return (self.path_separator, basename)
+
+  def JoinPaths(self, *paths):
+    """Mimics os.path.join using the specified path_separator.
+
+    Mimics os.path.join using the path_separator that was specified
+    for this FakeFilesystem.
+
+    Args:
+      *paths:  (str) Zero or more paths to join.
+
+    Returns:
+      (str) The paths joined by the path separator, starting with the last
+          absolute path in paths.
+    """
+    if len(paths) == 1:
+      return paths[0]
+    joined_path_segments = []
+    for path_segment in paths:
+      if path_segment.startswith(self.path_separator):
+        # An absolute path
+        joined_path_segments = [path_segment]
+      else:
+        if (joined_path_segments and
+            not joined_path_segments[-1].endswith(self.path_separator)):
+          joined_path_segments.append(self.path_separator)
+        if path_segment:
+          joined_path_segments.append(path_segment)
+    return ''.join(joined_path_segments)
+
+  def GetPathComponents(self, path):
+    """Breaks the path into a list of component names.
+
+    Does not include the root directory as a component, as all paths
+    are considered relative to the root directory for the FakeFilesystem.
+    Callers should basically follow this pattern:
+
+      file_path = self.NormalizePath(file_path)
+      path_components = self.GetPathComponents(file_path)
+      current_dir = self.root
+      for component in path_components:
+        if component not in current_dir.contents:
+          raise IOError
+        DoStuffWithComponent(curent_dir, component)
+        current_dir = current_dir.GetEntry(component)
+
+    Args:
+      path:  path to tokenize
+
+    Returns:
+      The list of names split from path
+    """
+    if not path or path == self.root.name:
+      return []
+    path_components = path.split(self.path_separator)
+    assert path_components
+    if not path_components[0]:
+      # This is an absolute path.
+      path_components = path_components[1:]
+    return path_components
+
+  def Exists(self, file_path):
+    """True if a path points to an existing file system object.
+
+    Args:
+      file_path:  path to examine
+
+    Returns:
+      bool(if object exists)
+
+    Raises:
+      TypeError: if file_path is None
+    """
+    if file_path is None:
+      raise TypeError
+    if not file_path:
+      return False
+    try:
+      file_path = self.ResolvePath(file_path)
+    except IOError:
+      return False
+    if file_path == self.root.name:
+      return True
+    path_components = self.GetPathComponents(file_path)
+    current_dir = self.root
+    for component in path_components:
+      if component not in current_dir.contents:
+        return False
+      current_dir = current_dir.contents[component]
+    return True
+
+  def ResolvePath(self, file_path):
+    """Follow a path, resolving symlinks.
+
+    ResolvePath traverses the filesystem along the specified file path,
+    resolving file names and symbolic links until all elements of the path are
+    exhausted, or we reach a file which does not exist.  If all the elements
+    are not consumed, they just get appended to the path resolved so far.
+    This gives us the path which is as resolved as it can be, even if the file
+    does not exist.
+
+    This behavior mimics Unix semantics, and is best shown by example.  Given a
+    file system that looks like this:
+
+          /a/b/
+          /a/b/c -> /a/b2          c is a symlink to /a/b2
+          /a/b2/x
+          /a/c   -> ../d
+          /a/x   -> y
+     Then:
+          /a/b/x      =>  /a/b/x
+          /a/c        =>  /a/d
+          /a/x        =>  /a/y
+          /a/b/c/d/e  =>  /a/b2/d/e
+
+    Args:
+      file_path:  path to examine
+
+    Returns:
+      resolved_path (string) or None
+
+    Raises:
+      TypeError: if file_path is None
+      IOError: if file_path is '' or a part of the path doesn't exist
+    """
+
+    def _ComponentsToPath(component_folders):
+      return '%s%s' % (self.path_separator,
+                       self.path_separator.join(component_folders))
+
+    def _ValidRelativePath(file_path):
+      while file_path and '/..' in file_path:
+        file_path = file_path[:file_path.rfind('/..')]
+        if not self.Exists(self.NormalizePath(file_path)):
+          return False
+      return True
+
+    def _FollowLink(link_path_components, link):
+      """Follow a link w.r.t. a path resolved so far.
+
+      The component is either a real file, which is a no-op, or a symlink.
+      In the case of a symlink, we have to modify the path as built up so far
+        /a/b => ../c   should yield /a/../c (which will normalize to /a/c)
+        /a/b => x      should yield /a/x
+        /a/b => /x/y/z should yield /x/y/z
+      The modified path may land us in a new spot which is itself a
+      link, so we may repeat the process.
+
+      Args:
+        link_path_components: The resolved path built up to the link so far.
+        link: The link object itself.
+
+      Returns:
+        (string) the updated path resolved after following the link.
+
+      Raises:
+        IOError: if there are too many levels of symbolic link
+      """
+      link_path = link.contents
+      # For links to absolute paths, we want to throw out everything in the
+      # path built so far and replace with the link.  For relative links, we
+      # have to append the link to what we have so far,
+      if not link_path.startswith(self.path_separator):
+        # Relative path.  Append remainder of path to what we have processed
+        # so far, excluding the name of the link itself.
+        # /a/b => ../c   should yield /a/../c (which will normalize to /c)
+        # /a/b => d should yield a/d
+        components = link_path_components[:-1]
+        components.append(link_path)
+        link_path = self.path_separator.join(components)
+      # Don't call self.NormalizePath(), as we don't want to prepend self.cwd.
+      return self.CollapsePath(link_path)
+
+    if file_path is None:
+      # file.open(None) raises TypeError, so mimic that.
+      raise TypeError('Expected file system path string, received None')
+    if not file_path or not _ValidRelativePath(file_path):
+      # file.open('') raises IOError, so mimic that, and validate that all
+      # parts of a relative path exist.
+      raise IOError(errno.ENOENT,
+                    'No such file or directory: \'%s\'' % file_path)
+    file_path = self.NormalizePath(file_path)
+    if file_path == self.root.name:
+      return file_path
+
+    current_dir = self.root
+    path_components = self.GetPathComponents(file_path)
+
+    resolved_components = []
+    link_depth = 0
+    while path_components:
+      component = path_components.pop(0)
+      resolved_components.append(component)
+      if component not in current_dir.contents:
+        # The component of the path at this point does not actually exist in
+        # the folder.   We can't resolve the path any more.  It is legal to link
+        # to a file that does not yet exist, so rather than raise an error, we
+        # just append the remaining components to what return path we have built
+        # so far and return that.
+        resolved_components.extend(path_components)
+        break
+      current_dir = current_dir.contents[component]
+
+      # Resolve any possible symlinks in the current path component.
+      if stat.S_ISLNK(current_dir.st_mode):
+        # This link_depth check is not really meant to be an accurate check.
+        # It is just a quick hack to prevent us from looping forever on
+        # cycles.
+        link_depth += 1
+        if link_depth > _MAX_LINK_DEPTH:
+          raise IOError(errno.EMLINK,
+                        'Too many levels of symbolic links: \'%s\'' %
+                        _ComponentsToPath(resolved_components))
+        link_path = _FollowLink(resolved_components, current_dir)
+
+        # Following the link might result in the complete replacement of the
+        # current_dir, so we evaluate the entire resulting path.
+        target_components = self.GetPathComponents(link_path)
+        path_components = target_components + path_components
+        resolved_components = []
+        current_dir = self.root
+    return _ComponentsToPath(resolved_components)
+
+  def GetObjectFromNormalizedPath(self, file_path):
+    """Searches for the specified filesystem object within the fake filesystem.
+
+    Args:
+      file_path: specifies target FakeFile object to retrieve, with a
+          path that has already been normalized/resolved
+
+    Returns:
+      the FakeFile object corresponding to file_path
+
+    Raises:
+      IOError: if the object is not found
+    """
+    if file_path == self.root.name:
+      return self.root
+    path_components = self.GetPathComponents(file_path)
+    target_object = self.root
+    try:
+      for component in path_components:
+        if not isinstance(target_object, FakeDirectory):
+          raise IOError(errno.ENOENT,
+                        'No such file or directory in fake filesystem',
+                        file_path)
+        target_object = target_object.GetEntry(component)
+    except KeyError:
+      raise IOError(errno.ENOENT,
+                    'No such file or directory in fake filesystem',
+                    file_path)
+    return target_object
+
+  def GetObject(self, file_path):
+    """Searches for the specified filesystem object within the fake filesystem.
+
+    Args:
+      file_path: specifies target FakeFile object to retrieve
+
+    Returns:
+      the FakeFile object corresponding to file_path
+
+    Raises:
+      IOError: if the object is not found
+    """
+    file_path = self.NormalizePath(file_path)
+    return self.GetObjectFromNormalizedPath(file_path)
+
+  def ResolveObject(self, file_path):
+    """Searches for the specified filesystem object, resolving all links.
+
+    Args:
+      file_path: specifies target FakeFile object to retrieve
+
+    Returns:
+      the FakeFile object corresponding to file_path
+
+    Raises:
+      IOError: if the object is not found
+    """
+    return self.GetObjectFromNormalizedPath(self.ResolvePath(file_path))
+
+  def LResolveObject(self, path):
+    """Searches for the specified object, resolving only parent links.
+
+    This is analogous to the stat/lstat difference.  This resolves links *to*
+    the object but not of the final object itself.
+
+    Args:
+      path: specifies target FakeFile object to retrieve
+
+    Returns:
+      the FakeFile object corresponding to path
+
+    Raises:
+      IOError: if the object is not found
+    """
+    if path == self.root.name:
+      # The root directory will never be a link
+      return self.root
+    parent_directory, child_name = self.SplitPath(path)
+    if not parent_directory:
+      parent_directory = self.cwd
+    try:
+      parent_obj = self.ResolveObject(parent_directory)
+      assert parent_obj
+      if not isinstance(parent_obj, FakeDirectory):
+        raise IOError(errno.ENOENT,
+                      'No such file or directory in fake filesystem',
+                      path)
+      return parent_obj.GetEntry(child_name)
+    except KeyError:
+      raise IOError(errno.ENOENT,
+                    'No such file or directory in the fake filesystem',
+                    path)
+
+  def AddObject(self, file_path, file_object):
+    """Add a fake file or directory into the filesystem at file_path.
+
+    Args:
+      file_path: the path to the file to be added relative to self
+      file_object: file or directory to add
+
+    Raises:
+      IOError: if file_path does not correspond to a directory
+    """
+    try:
+      target_directory = self.GetObject(file_path)
+      target_directory.AddEntry(file_object)
+    except AttributeError:
+      raise IOError(errno.ENOTDIR,
+                    'Not a directory in the fake filesystem',
+                    file_path)
+
+  def RemoveObject(self, file_path):
+    """Remove an existing file or directory.
+
+    Args:
+      file_path: the path to the file relative to self
+
+    Raises:
+      IOError: if file_path does not correspond to an existing file, or if part
+        of the path refers to something other than a directory
+      OSError: if the directory is in use (eg, if it is '/')
+    """
+    if file_path == self.root.name:
+      raise OSError(errno.EBUSY, 'Fake device or resource busy',
+                    file_path)
+    try:
+      dirname, basename = self.SplitPath(file_path)
+      target_directory = self.GetObject(dirname)
+      target_directory.RemoveEntry(basename)
+    except KeyError:
+      raise IOError(errno.ENOENT,
+                    'No such file or directory in the fake filesystem',
+                    file_path)
+    except AttributeError:
+      raise IOError(errno.ENOTDIR,
+                    'Not a directory in the fake filesystem',
+                    file_path)
+
+  def CreateDirectory(self, directory_path, perm_bits=PERM_DEF, inode=None):
+    """Creates directory_path, and all the parent directories.
+
+    Helper method to set up your test faster
+
+    Args:
+      directory_path:  directory to create
+      perm_bits: permission bits
+      inode: inode of directory
+
+    Returns:
+      the newly created FakeDirectory object
+
+    Raises:
+      OSError:  if the directory already exists
+    """
+    directory_path = self.NormalizePath(directory_path)
+    if self.Exists(directory_path):
+      raise OSError(errno.EEXIST,
+                    'Directory exists in fake filesystem',
+                    directory_path)
+    path_components = self.GetPathComponents(directory_path)
+    current_dir = self.root
+
+    for component in path_components:
+      if component not in current_dir.contents:
+        new_dir = FakeDirectory(component, perm_bits)
+        current_dir.AddEntry(new_dir)
+        current_dir = new_dir
+      else:
+        current_dir = current_dir.contents[component]
+
+    current_dir.SetIno(inode)
+    return current_dir
+
+  def CreateFile(self, file_path, st_mode=stat.S_IFREG | PERM_DEF_FILE,
+                 contents='', st_size=None, create_missing_dirs=True,
+                 apply_umask=False, inode=None):
+    """Creates file_path, including all the parent directories along the way.
+
+    Helper method to set up your test faster.
+
+    Args:
+      file_path: path to the file to create
+      st_mode: the stat.S_IF constant representing the file type
+      contents: the contents of the file
+      st_size: file size; only valid if contents=None
+      create_missing_dirs: if True, auto create missing directories
+      apply_umask: whether or not the current umask must be applied on st_mode
+      inode: inode of the file
+
+    Returns:
+      the newly created FakeFile object
+
+    Raises:
+      IOError: if the file already exists
+      IOError: if the containing directory is required and missing
+    """
+    file_path = self.NormalizePath(file_path)
+    if self.Exists(file_path):
+      raise IOError(errno.EEXIST,
+                    'File already exists in fake filesystem',
+                    file_path)
+    parent_directory, new_file = self.SplitPath(file_path)
+    if not parent_directory:
+      parent_directory = self.cwd
+    if not self.Exists(parent_directory):
+      if not create_missing_dirs:
+        raise IOError(errno.ENOENT, 'No such fake directory', parent_directory)
+      self.CreateDirectory(parent_directory)
+    if apply_umask:
+      st_mode &= ~self.umask
+    file_object = FakeFile(new_file, st_mode, contents)
+    file_object.SetIno(inode)
+    self.AddObject(parent_directory, file_object)
+
+    # set the size if st_size is given
+    if not contents and st_size is not None:
+      try:
+        file_object.SetLargeFileSize(st_size)
+      except IOError:
+        self.RemoveObject(file_path)
+        raise
+
+    return file_object
+
+  def CreateLink(self, file_path, link_target):
+    """Creates the specified symlink, pointed at the specified link target.
+
+    Args:
+      file_path:  path to the symlink to create
+      link_target:  the target of the symlink
+
+    Returns:
+      the newly created FakeFile object
+
+    Raises:
+      IOError:  if the file already exists
+    """
+    resolved_file_path = self.ResolvePath(file_path)
+    return self.CreateFile(resolved_file_path, st_mode=stat.S_IFLNK | PERM_DEF,
+                           contents=link_target)
+
+  def __str__(self):
+    return str(self.root)
+
+
+class FakePathModule(object):
+  """Faked os.path module replacement.
+
+  FakePathModule should *only* be instantiated by FakeOsModule.  See the
+  FakeOsModule docstring for details.
+  """
+  _OS_PATH_COPY = CopyModule(os.path)
+
+  def __init__(self, filesystem, os_module=None):
+    """Init.
+
+    Args:
+      filesystem:  FakeFilesystem used to provide file system information
+      os_module: (deprecated) FakeOsModule to assign to self.os
+    """
+    self.filesystem = filesystem
+    self._os_path = self._OS_PATH_COPY
+    if os_module is None:
+      warnings.warn(FAKE_PATH_MODULE_DEPRECATION, DeprecationWarning,
+                    stacklevel=2)
+    self._os_path.os = self.os = os_module
+    self.sep = self.filesystem.path_separator
+
+  def exists(self, path):
+    """Determines whether the file object exists within the fake filesystem.
+
+    Args:
+      path:  path to the file object
+
+    Returns:
+      bool (if file exists)
+    """
+    return self.filesystem.Exists(path)
+
+  def lexists(self, path):
+    """Test whether a path exists.  Returns True for broken symbolic links.
+
+    Args:
+      path:  path to the symlnk object
+
+    Returns:
+      bool (if file exists)
+    """
+    return self.exists(path) or self.islink(path)
+
+  def getsize(self, path):
+    """Return the file object size in bytes.
+
+    Args:
+      path:  path to the file object
+
+    Returns:
+      file size in bytes
+    """
+    file_obj = self.filesystem.GetObject(path)
+    return file_obj.st_size
+
+  def _istype(self, path, st_flag):
+    """Helper function to implement isdir(), islink(), etc.
+
+    See the stat(2) man page for valid stat.S_I* flag values
+
+    Args:
+      path:  path to file to stat and test
+      st_flag:  the stat.S_I* flag checked for the file's st_mode
+
+    Returns:
+      boolean (the st_flag is set in path's st_mode)
+
+    Raises:
+      TypeError: if path is None
+    """
+    if path is None:
+      raise TypeError
+    try:
+      obj = self.filesystem.ResolveObject(path)
+      if obj:
+        return stat.S_IFMT(obj.st_mode) == st_flag
+    except IOError:
+      return False
+    return False
+
+  def isabs(self, path):
+    if self.filesystem.path_separator == os.path.sep:
+      # Pass through to os.path.isabs, which on Windows has special
+      # handling for a leading drive letter.
+      return self._os_path.isabs(path)
+    else:
+      return path.startswith(self.filesystem.path_separator)
+
+  def isdir(self, path):
+    """Determines if path identifies a directory."""
+    return self._istype(path, stat.S_IFDIR)
+
+  def isfile(self, path):
+    """Determines if path identifies a regular file."""
+    return self._istype(path, stat.S_IFREG)
+
+  def islink(self, path):
+    """Determines if path identifies a symbolic link.
+
+    Args:
+      path: path to filesystem object.
+
+    Returns:
+      boolean (the st_flag is set in path's st_mode)
+
+    Raises:
+      TypeError: if path is None
+    """
+    if path is None:
+      raise TypeError
+    try:
+      link_obj = self.filesystem.LResolveObject(path)
+      return stat.S_IFMT(link_obj.st_mode) == stat.S_IFLNK
+    except IOError:
+      return False
+    except KeyError:
+      return False
+    return False
+
+  def getmtime(self, path):
+    """Returns the mtime of the file."""
+    try:
+      file_obj = self.filesystem.GetObject(path)
+    except IOError as e:
+      raise OSError(errno.ENOENT, str(e))
+    return file_obj.st_mtime
+
+  def abspath(self, path):
+    """Return the absolute version of a path."""
+    if not self.isabs(path):
+      if sys.version_info < (3, 0) and isinstance(path, unicode):
+        cwd = self.os.getcwdu()
+      else:
+        cwd = self.os.getcwd()
+      path = self.join(cwd, path)
+    return self.normpath(path)
+
+  def join(self, *p):
+    """Returns the completed path with a separator of the parts."""
+    return self.filesystem.JoinPaths(*p)
+
+  def normpath(self, path):
+    """Normalize path, eliminating double slashes, etc."""
+    return self.filesystem.CollapsePath(path)
+
+  if _is_windows:
+
+    def relpath(self, path, start=None):
+      """ntpath.relpath() needs the cwd passed in the start argument."""
+      if start is None:
+        start = self.filesystem.cwd
+      path = self._os_path.relpath(path, start)
+      return path.replace(self._os_path.sep, self.filesystem.path_separator)
+
+    realpath = abspath
+
+  def __getattr__(self, name):
+    """Forwards any non-faked calls to os.path."""
+    return self._os_path.__dict__[name]
+
+
+class FakeOsModule(object):
+  """Uses FakeFilesystem to provide a fake os module replacement.
+
+  Do not create os.path separately from os, as there is a necessary circular
+  dependency between os and os.path to replicate the behavior of the standard
+  Python modules.  What you want to do is to just let FakeOsModule take care of
+  os.path setup itself.
+
+  # You always want to do this.
+  filesystem = fake_filesystem.FakeFilesystem()
+  my_os_module = fake_filesystem.FakeOsModule(filesystem)
+  """
+
+  def __init__(self, filesystem, os_path_module=None):
+    """Also exposes self.path (to fake os.path).
+
+    Args:
+      filesystem:  FakeFilesystem used to provide file system information
+      os_path_module: (deprecated) optional FakePathModule instance
+    """
+    self.filesystem = filesystem
+    self.sep = filesystem.path_separator
+    self._os_module = os
+    if os_path_module is None:
+      self.path = FakePathModule(self.filesystem, self)
+    else:
+      warnings.warn(FAKE_PATH_MODULE_DEPRECATION, DeprecationWarning,
+                    stacklevel=2)
+      self.path = os_path_module
+    if sys.version_info < (3, 0):
+      self.fdopen = self._fdopen_ver2
+    else:
+      self.fdopen = self._fdopen
+
+  def _fdopen(self, *args, **kwargs):
+    """Redirector to open() builtin function.
+
+    Args:
+      *args: pass through args
+      **kwargs: pass through kwargs
+
+    Returns:
+      File object corresponding to file_des.
+
+    Raises:
+      TypeError: if file descriptor is not an integer.
+    """
+    if not isinstance(args[0], int):
+      raise TypeError('an integer is required')
+    return FakeFileOpen(self.filesystem)(*args, **kwargs)
+
+  def _fdopen_ver2(self, file_des, mode='r', bufsize=None):
+    """Returns an open file object connected to the file descriptor file_des.
+
+    Args:
+      file_des: An integer file descriptor for the file object requested.
+      mode: additional file flags. Currently checks to see if the mode matches
+        the mode of the requested file object.
+      bufsize: ignored. (Used for signature compliance with __builtin__.fdopen)
+
+    Returns:
+      File object corresponding to file_des.
+
+    Raises:
+      OSError: if bad file descriptor or incompatible mode is given.
+      TypeError: if file descriptor is not an integer.
+    """
+    if not isinstance(file_des, int):
+      raise TypeError('an integer is required')
+
+    try:
+      return FakeFileOpen(self.filesystem).Call(file_des, mode=mode)
+    except IOError as e:
+      raise OSError(e)
+
+  def open(self, file_path, flags, mode=None):
+    """Returns the file descriptor for a FakeFile.
+
+    WARNING: This implementation only implements creating a file. Please fill
+    out the remainder for your needs.
+
+    Args:
+      file_path: the path to the file
+      flags: low-level bits to indicate io operation
+      mode: bits to define default permissions
+
+    Returns:
+      A file descriptor.
+
+    Raises:
+      OSError: if the path cannot be found
+      ValueError: if invalid mode is given
+      NotImplementedError: if an unsupported flag is passed in
+    """
+    if flags & os.O_CREAT:
+      fake_file = FakeFileOpen(self.filesystem)(file_path, 'w')
+      if mode:
+        self.chmod(file_path, mode)
+      return fake_file.fileno()
+    else:
+      raise NotImplementedError('FakeOsModule.open')
+
+  def close(self, file_des):
+    """Closes a file descriptor.
+
+    Args:
+      file_des: An integer file descriptor for the file object requested.
+
+    Raises:
+      OSError: bad file descriptor.
+      TypeError: if file descriptor is not an integer.
+    """
+    fh = self.filesystem.GetOpenFile(file_des)
+    fh.close()
+
+  def read(self, file_des, num_bytes):
+    """Reads number of bytes from a file descriptor, returns bytes read.
+
+    Args:
+      file_des: An integer file descriptor for the file object requested.
+      num_bytes: Number of bytes to read from file.
+
+    Returns:
+      Bytes read from file.
+
+    Raises:
+      OSError: bad file descriptor.
+      TypeError: if file descriptor is not an integer.
+    """
+    fh = self.filesystem.GetOpenFile(file_des)
+    return fh.read(num_bytes)
+
+  def write(self, file_des, contents):
+    """Writes string to file descriptor, returns number of bytes written.
+
+    Args:
+      file_des: An integer file descriptor for the file object requested.
+      contents: String of bytes to write to file.
+
+    Returns:
+      Number of bytes written.
+
+    Raises:
+      OSError: bad file descriptor.
+      TypeError: if file descriptor is not an integer.
+    """
+    fh = self.filesystem.GetOpenFile(file_des)
+    fh.write(contents)
+    fh.flush()
+    return len(contents)
+
+  def fstat(self, file_des):
+    """Returns the os.stat-like tuple for the FakeFile object of file_des.
+
+    Args:
+      file_des:  file descriptor of filesystem object to retrieve
+
+    Returns:
+      the os.stat_result object corresponding to entry_path
+
+    Raises:
+      OSError: if the filesystem object doesn't exist.
+    """
+    # stat should return the tuple representing return value of os.stat
+    stats = self.filesystem.GetOpenFile(file_des).GetObject()
+    st_obj = os.stat_result((stats.st_mode, stats.st_ino, stats.st_dev,
+                             stats.st_nlink, stats.st_uid, stats.st_gid,
+                             stats.st_size, stats.st_atime,
+                             stats.st_mtime, stats.st_ctime))
+    return st_obj
+
+  def _ConfirmDir(self, target_directory):
+    """Tests that the target is actually a directory, raising OSError if not.
+
+    Args:
+      target_directory:  path to the target directory within the fake
+        filesystem
+
+    Returns:
+      the FakeFile object corresponding to target_directory
+
+    Raises:
+      OSError:  if the target is not a directory
+    """
+    try:
+      directory = self.filesystem.GetObject(target_directory)
+    except IOError as e:
+      raise OSError(e.errno, e.strerror, target_directory)
+    if not directory.st_mode & stat.S_IFDIR:
+      raise OSError(errno.ENOTDIR,
+                    'Fake os module: not a directory',
+                    target_directory)
+    return directory
+
+  def umask(self, new_mask):
+    """Change the current umask.
+
+    Args:
+      new_mask: An integer.
+
+    Returns:
+      The old mask.
+
+    Raises:
+      TypeError: new_mask is of an invalid type.
+    """
+    if not isinstance(new_mask, int):
+      raise TypeError('an integer is required')
+    old_umask = self.filesystem.umask
+    self.filesystem.umask = new_mask
+    return old_umask
+
+  def chdir(self, target_directory):
+    """Change current working directory to target directory.
+
+    Args:
+      target_directory:  path to new current working directory
+
+    Raises:
+      OSError: if user lacks permission to enter the argument directory or if
+               the target is not a directory
+    """
+    target_directory = self.filesystem.ResolvePath(target_directory)
+    self._ConfirmDir(target_directory)
+    directory = self.filesystem.GetObject(target_directory)
+    # A full implementation would check permissions all the way up the tree.
+    if not directory.st_mode | PERM_EXE:
+      raise OSError(errno.EACCES, 'Fake os module: permission denied',
+                    directory)
+    self.filesystem.cwd = target_directory
+
+  def getcwd(self):
+    """Return current working directory."""
+    return self.filesystem.cwd
+
+  def getcwdu(self):
+    """Return current working directory. Deprecated in Python 3."""
+    if sys.version_info >= (3, 0):
+      raise AttributeError('no attribute getcwdu')
+    return unicode(self.filesystem.cwd)
+
+  def listdir(self, target_directory):
+    """Returns a sorted list of filenames in target_directory.
+
+    Args:
+      target_directory:  path to the target directory within the fake
+        filesystem
+
+    Returns:
+      a sorted list of file names within the target directory
+
+    Raises:
+      OSError:  if the target is not a directory
+    """
+    target_directory = self.filesystem.ResolvePath(target_directory)
+    directory = self._ConfirmDir(target_directory)
+    return sorted(directory.contents)
+
+  def _ClassifyDirectoryContents(self, root):
+    """Classify contents of a directory as files/directories.
+
+    Args:
+      root: (str) Directory to examine.
+
+    Returns:
+      (tuple) A tuple consisting of three values: the directory examined, a
+      list containing all of the directory entries, and a list containing all
+      of the non-directory entries.  (This is the same format as returned by
+      the os.walk generator.)
+
+    Raises:
+      Nothing on its own, but be ready to catch exceptions generated by
+      underlying mechanisms like os.listdir.
+    """
+    dirs = []
+    files = []
+    for entry in self.listdir(root):
+      if self.path.isdir(self.path.join(root, entry)):
+        dirs.append(entry)
+      else:
+        files.append(entry)
+    return (root, dirs, files)
+
+  def walk(self, top, topdown=True, onerror=None):
+    """Performs an os.walk operation over the fake filesystem.
+
+    Args:
+      top:  root directory from which to begin walk
+      topdown:  determines whether to return the tuples with the root as the
+        first entry (True) or as the last, after all the child directory
+        tuples (False)
+      onerror:  if not None, function which will be called to handle the
+        os.error instance provided when os.listdir() fails
+
+    Yields:
+      (path, directories, nondirectories) for top and each of its
+      subdirectories.  See the documentation for the builtin os module for
+      further details.
+    """
+    top = self.path.normpath(top)
+    try:
+      top_contents = self._ClassifyDirectoryContents(top)
+    except OSError as e:
+      top_contents = None
+      if onerror is not None:
+        onerror(e)
+
+    if top_contents is not None:
+      if topdown:
+        yield top_contents
+
+      for directory in top_contents[1]:
+        for contents in self.walk(self.path.join(top, directory),
+                                  topdown=topdown, onerror=onerror):
+          yield contents
+
+      if not topdown:
+        yield top_contents
+
+  def readlink(self, path):
+    """Reads the target of a symlink.
+
+    Args:
+      path:  symlink to read the target of
+
+    Returns:
+      the string representing the path to which the symbolic link points.
+
+    Raises:
+      TypeError: if path is None
+      OSError: (with errno=ENOENT) if path is not a valid path, or
+               (with errno=EINVAL) if path is valid, but is not a symlink
+    """
+    if path is None:
+      raise TypeError
+    try:
+      link_obj = self.filesystem.LResolveObject(path)
+    except IOError:
+      raise OSError(errno.ENOENT, 'Fake os module: path does not exist', path)
+    if stat.S_IFMT(link_obj.st_mode) != stat.S_IFLNK:
+      raise OSError(errno.EINVAL, 'Fake os module: not a symlink', path)
+    return link_obj.contents
+
+  def stat(self, entry_path):
+    """Returns the os.stat-like tuple for the FakeFile object of entry_path.
+
+    Args:
+      entry_path:  path to filesystem object to retrieve
+
+    Returns:
+      the os.stat_result object corresponding to entry_path
+
+    Raises:
+      OSError: if the filesystem object doesn't exist.
+    """
+    # stat should return the tuple representing return value of os.stat
+    try:
+      stats = self.filesystem.ResolveObject(entry_path)
+      st_obj = os.stat_result((stats.st_mode, stats.st_ino, stats.st_dev,
+                               stats.st_nlink, stats.st_uid, stats.st_gid,
+                               stats.st_size, stats.st_atime,
+                               stats.st_mtime, stats.st_ctime))
+      return st_obj
+    except IOError as io_error:
+      raise OSError(io_error.errno, io_error.strerror, entry_path)
+
+  def lstat(self, entry_path):
+    """Returns the os.stat-like tuple for entry_path, not following symlinks.
+
+    Args:
+      entry_path:  path to filesystem object to retrieve
+
+    Returns:
+      the os.stat_result object corresponding to entry_path
+
+    Raises:
+      OSError: if the filesystem object doesn't exist.
+    """
+    # stat should return the tuple representing return value of os.stat
+    try:
+      stats = self.filesystem.LResolveObject(entry_path)
+      st_obj = os.stat_result((stats.st_mode, stats.st_ino, stats.st_dev,
+                               stats.st_nlink, stats.st_uid, stats.st_gid,
+                               stats.st_size, stats.st_atime,
+                               stats.st_mtime, stats.st_ctime))
+      return st_obj
+    except IOError as io_error:
+      raise OSError(io_error.errno, io_error.strerror, entry_path)
+
+  def remove(self, path):
+    """Removes the FakeFile object representing the specified file."""
+    path = self.filesystem.NormalizePath(path)
+    if self.path.isdir(path) and not self.path.islink(path):
+      raise OSError(errno.EISDIR, "Is a directory: '%s'" % path)
+    try:
+      self.filesystem.RemoveObject(path)
+    except IOError as e:
+      raise OSError(e.errno, e.strerror, e.filename)
+
+  # As per the documentation unlink = remove.
+  unlink = remove
+
+  def rename(self, old_file, new_file):
+    """Adds a FakeFile object at new_file containing contents of old_file.
+
+    Also removes the FakeFile object for old_file, and replaces existing
+    new_file object, if one existed.
+
+    Args:
+      old_file:  path to filesystem object to rename
+      new_file:  path to where the filesystem object will live after this call
+
+    Raises:
+      OSError:  if old_file does not exist.
+      IOError:  if dirname(new_file) does not exist
+    """
+    old_file = self.filesystem.NormalizePath(old_file)
+    new_file = self.filesystem.NormalizePath(new_file)
+    if not self.filesystem.Exists(old_file):
+      raise OSError(errno.ENOENT,
+                    'Fake os object: can not rename nonexistent file '
+                    'with name',
+                    old_file)
+    if self.filesystem.Exists(new_file):
+      if old_file == new_file:
+        return None  # Nothing to do here.
+      else:
+        self.remove(new_file)
+    old_dir, old_name = self.path.split(old_file)
+    new_dir, new_name = self.path.split(new_file)
+    if not self.filesystem.Exists(new_dir):
+      raise IOError(errno.ENOENT, 'No such fake directory', new_dir)
+    old_dir_object = self.filesystem.ResolveObject(old_dir)
+    old_object = old_dir_object.GetEntry(old_name)
+    old_object_mtime = old_object.st_mtime
+    new_dir_object = self.filesystem.ResolveObject(new_dir)
+    if old_object.st_mode & stat.S_IFDIR:
+      old_object.name = new_name
+      new_dir_object.AddEntry(old_object)
+      old_dir_object.RemoveEntry(old_name)
+    else:
+      self.filesystem.CreateFile(new_file,
+                                 st_mode=old_object.st_mode,
+                                 contents=old_object.contents,
+                                 create_missing_dirs=False)
+      self.remove(old_file)
+    new_object = self.filesystem.GetObject(new_file)
+    new_object.SetMTime(old_object_mtime)
+    self.chown(new_file, old_object.st_uid, old_object.st_gid)
+
+  def rmdir(self, target_directory):
+    """Remove a leaf Fake directory.
+
+    Args:
+      target_directory: (str) Name of directory to remove.
+
+    Raises:
+      OSError: if target_directory does not exist or is not a directory,
+      or as per FakeFilesystem.RemoveObject. Cannot remove '.'.
+    """
+    if target_directory == '.':
+      raise OSError(errno.EINVAL, 'Invalid argument: \'.\'')
+    target_directory = self.filesystem.NormalizePath(target_directory)
+    if self._ConfirmDir(target_directory):
+      if self.listdir(target_directory):
+        raise OSError(errno.ENOTEMPTY, 'Fake Directory not empty',
+                      target_directory)
+      try:
+        self.filesystem.RemoveObject(target_directory)
+      except IOError as e:
+        raise OSError(e.errno, e.strerror, e.filename)
+
+  def removedirs(self, target_directory):
+    """Remove a leaf Fake directory and all empty intermediate ones."""
+    target_directory = self.filesystem.NormalizePath(target_directory)
+    directory = self._ConfirmDir(target_directory)
+    if directory.contents:
+      raise OSError(errno.ENOTEMPTY, 'Fake Directory not empty',
+                    self.path.basename(target_directory))
+    else:
+      self.rmdir(target_directory)
+    head, tail = self.path.split(target_directory)
+    if not tail:
+      head, tail = self.path.split(head)
+    while head and tail:
+      head_dir = self._ConfirmDir(head)
+      if head_dir.contents:
+        break
+      self.rmdir(head)
+      head, tail = self.path.split(head)
+
+  def mkdir(self, dir_name, mode=PERM_DEF):
+    """Create a leaf Fake directory.
+
+    Args:
+      dir_name: (str) Name of directory to create.  Relative paths are assumed
+        to be relative to '/'.
+      mode: (int) Mode to create directory with.  This argument defaults to
+        0o777.  The umask is applied to this mode.
+
+    Raises:
+      OSError: if the directory name is invalid or parent directory is read only
+      or as per FakeFilesystem.AddObject.
+    """
+    if dir_name.endswith(self.sep):
+      dir_name = dir_name[:-1]
+
+    parent_dir, _ = self.path.split(dir_name)
+    if parent_dir:
+      base_dir = self.path.normpath(parent_dir)
+      if parent_dir.endswith(self.sep + '..'):
+        base_dir, unused_dotdot, _ = parent_dir.partition(self.sep + '..')
+      if not self.filesystem.Exists(base_dir):
+        raise OSError(errno.ENOENT, 'No such fake directory', base_dir)
+
+    dir_name = self.filesystem.NormalizePath(dir_name)
+    if self.filesystem.Exists(dir_name):
+      raise OSError(errno.EEXIST, 'Fake object already exists', dir_name)
+    head, tail = self.path.split(dir_name)
+    directory_object = self.filesystem.GetObject(head)
+    if not directory_object.st_mode & PERM_WRITE:
+      raise OSError(errno.EACCES, 'Permission Denied', dir_name)
+
+    self.filesystem.AddObject(
+        head, FakeDirectory(tail, mode & ~self.filesystem.umask))
+
+  def makedirs(self, dir_name, mode=PERM_DEF):
+    """Create a leaf Fake directory + create any non-existent parent dirs.
+
+    Args:
+      dir_name: (str) Name of directory to create.
+      mode: (int) Mode to create directory (and any necessary parent
+        directories) with. This argument defaults to 0o777.  The umask is
+        applied to this mode.
+
+    Raises:
+      OSError: if the directory already exists or as per
+      FakeFilesystem.CreateDirectory
+    """
+    dir_name = self.filesystem.NormalizePath(dir_name)
+    path_components = self.filesystem.GetPathComponents(dir_name)
+
+    # Raise a permission denied error if the first existing directory is not
+    # writeable.
+    current_dir = self.filesystem.root
+    for component in path_components:
+      if component not in current_dir.contents:
+        if not current_dir.st_mode & PERM_WRITE:
+          raise OSError(errno.EACCES, 'Permission Denied', dir_name)
+        else:
+          break
+      else:
+        current_dir = current_dir.contents[component]
+
+    self.filesystem.CreateDirectory(dir_name, mode & ~self.filesystem.umask)
+
+  def access(self, path, mode):
+    """Check if a file exists and has the specified permissions.
+
+    Args:
+      path: (str) Path to the file.
+      mode: (int) Permissions represented as a bitwise-OR combination of
+          os.F_OK, os.R_OK, os.W_OK, and os.X_OK.
+    Returns:
+      boolean, True if file is accessible, False otherwise
+    """
+    try:
+      st = self.stat(path)
+    except OSError as os_error:
+      if os_error.errno == errno.ENOENT:
+        return False
+      raise
+    return (mode & ((st.st_mode >> 6) & 7)) == mode
+
+  def chmod(self, path, mode):
+    """Change the permissions of a file as encoded in integer mode.
+
+    Args:
+      path: (str) Path to the file.
+      mode: (int) Permissions
+    """
+    try:
+      file_object = self.filesystem.GetObject(path)
+    except IOError as io_error:
+      if io_error.errno == errno.ENOENT:
+        raise OSError(errno.ENOENT,
+                      'No such file or directory in fake filesystem',
+                      path)
+      raise
+    file_object.st_mode = ((file_object.st_mode & ~PERM_ALL) |
+                           (mode & PERM_ALL))
+    file_object.st_ctime = int(time.time())
+
+  def utime(self, path, times):
+    """Change the access and modified times of a file.
+
+    Args:
+      path: (str) Path to the file.
+      times: 2-tuple of numbers, of the form (atime, mtime) which is used to set
+          the access and modified times, respectively. If None, file's access
+          and modified times are set to the current time.
+
+    Raises:
+      TypeError: If anything other than integers is specified in passed tuple or
+          number of elements in the tuple is not equal to 2.
+    """
+    try:
+      file_object = self.filesystem.GetObject(path)
+    except IOError as io_error:
+      if io_error.errno == errno.ENOENT:
+        raise OSError(errno.ENOENT,
+                      'No such file or directory in fake filesystem',
+                      path)
+      raise
+    if times is None:
+      file_object.st_atime = int(time.time())
+      file_object.st_mtime = int(time.time())
+    else:
+      if len(times) != 2:
+        raise TypeError('utime() arg 2 must be a tuple (atime, mtime)')
+      for t in times:
+        if not isinstance(t, (int, float)):
+          raise TypeError('an integer is required')
+
+      file_object.st_atime = times[0]
+      file_object.st_mtime = times[1]
+
+  def chown(self, path, uid, gid):
+    """Set ownership of a faked file.
+
+    Args:
+      path: (str) Path to the file or directory.
+      uid: (int) Numeric uid to set the file or directory to.
+      gid: (int) Numeric gid to set the file or directory to.
+    """
+    try:
+      file_object = self.filesystem.GetObject(path)
+    except IOError as io_error:
+      if io_error.errno == errno.ENOENT:
+        raise OSError(errno.ENOENT,
+                      'No such file or directory in fake filesystem',
+                      path)
+      raise
+    if uid != -1:
+      file_object.st_uid = uid
+    if gid != -1:
+      file_object.st_gid = gid
+
+  def mknod(self, filename, mode=None, device=None):
+    """Create a filesystem node named 'filename'.
+
+    Does not support device special files or named pipes as the real os
+    module does.
+
+    Args:
+      filename: (str) Name of the file to create
+      mode: (int) permissions to use and type of file to be created.
+        Default permissions are 0o666.  Only the stat.S_IFREG file type
+        is supported by the fake implementation.  The umask is applied
+        to this mode.
+      device: not supported in fake implementation
+
+    Raises:
+      OSError: if called with unsupported options or the file can not be
+      created.
+    """
+    if mode is None:
+      mode = stat.S_IFREG | PERM_DEF_FILE
+    if device or not mode & stat.S_IFREG:
+      raise OSError(errno.EINVAL,
+                    'Fake os mknod implementation only supports '
+                    'regular files.')
+
+    head, tail = self.path.split(filename)
+    if not tail:
+      if self.filesystem.Exists(head):
+        raise OSError(errno.EEXIST, 'Fake filesystem: %s: %s' % (
+            os.strerror(errno.EEXIST), filename))
+      raise OSError(errno.ENOENT, 'Fake filesystem: %s: %s' % (
+          os.strerror(errno.ENOENT), filename))
+    if tail == '.' or tail == '..' or self.filesystem.Exists(filename):
+      raise OSError(errno.EEXIST, 'Fake fileystem: %s: %s' % (
+          os.strerror(errno.EEXIST), filename))
+    try:
+      self.filesystem.AddObject(head, FakeFile(tail,
+                                               mode & ~self.filesystem.umask))
+    except IOError:
+      raise OSError(errno.ENOTDIR, 'Fake filesystem: %s: %s' % (
+          os.strerror(errno.ENOTDIR), filename))
+
+  def symlink(self, link_target, path):
+    """Creates the specified symlink, pointed at the specified link target.
+
+    Args:
+      link_target:  the target of the symlink
+      path:  path to the symlink to create
+
+    Returns:
+      None
+
+    Raises:
+      IOError:  if the file already exists
+    """
+    self.filesystem.CreateLink(path, link_target)
+
+  # pylint: disable-msg=C6002
+  # TODO: Link doesn't behave like os.link, this needs to be fixed properly.
+  link = symlink
+
+  def __getattr__(self, name):
+    """Forwards any unfaked calls to the standard os module."""
+    return getattr(self._os_module, name)
+
+
+class FakeFileOpen(object):
+  """Faked file() and open() function replacements.
+
+  Returns FakeFile objects in a FakeFilesystem in place of the file()
+  or open() function.
+  """
+
+  def __init__(self, filesystem, delete_on_close=False):
+    """init.
+
+    Args:
+      filesystem:  FakeFilesystem used to provide file system information
+      delete_on_close:  optional boolean, deletes file on close()
+    """
+    self.filesystem = filesystem
+    self._delete_on_close = delete_on_close
+
+  def __call__(self, *args, **kwargs):
+    """Redirects calls to file() or open() to appropriate method."""
+    if sys.version_info < (3, 0):
+      return self._call_ver2(*args, **kwargs)
+    else:
+      return self.Call(*args, **kwargs)
+
+  def _call_ver2(self, file_path, mode='r', buffering=-1, flags=None):
+    """Limits args of open() or file() for Python 2.x versions."""
+    # Backwards compatibility, mode arg used to be named flags
+    mode = flags or mode
+    return self.Call(file_path, mode, buffering)
+
+  def Call(self, file_, mode='r', buffering=-1, encoding=None,
+           errors=None, newline=None, closefd=True, opener=None):
+    """Returns a StringIO object with the contents of the target file object.
+
+    Args:
+      file_: path to target file or a file descriptor
+      mode: additional file modes. All r/w/a r+/w+/a+ modes are supported.
+        't', and 'U' are ignored, e.g., 'wU' is treated as 'w'. 'b' sets
+        binary mode, no end of line translations in StringIO.
+      buffering: ignored. (Used for signature compliance with __builtin__.open)
+      encoding: ignored, strings have no encoding
+      errors: ignored, this relates to encoding
+      newline: controls universal newlines, passed to StringIO object
+      closefd: if a file descriptor rather than file name is passed, and set
+        to false, then the file descriptor is kept open when file is closed
+      opener: not supported
+
+    Returns:
+      a StringIO object containing the contents of the target file
+
+    Raises:
+      IOError: if the target object is a directory, the path is invalid or
+        permission is denied.
+    """
+    orig_modes = mode  # Save original mdoes for error messages.
+    # Binary mode for non 3.x or set by mode
+    binary = sys.version_info < (3, 0) or 'b' in mode
+    # Normalize modes. Ignore 't' and 'U'.
+    mode = mode.replace('t', '').replace('b', '')
+    mode = mode.replace('rU', 'r').replace('U', 'r')
+
+    if mode not in _OPEN_MODE_MAP:
+      raise IOError('Invalid mode: %r' % orig_modes)
+
+    must_exist, need_read, need_write, truncate, append = _OPEN_MODE_MAP[mode]
+
+    file_object = None
+    filedes = None
+    # opening a file descriptor
+    if isinstance(file_, int):
+      filedes = file_
+      file_object = self.filesystem.GetOpenFile(filedes).GetObject()
+      file_path = file_object.name
+    else:
+      file_path = file_
+      real_path = self.filesystem.ResolvePath(file_path)
+      if self.filesystem.Exists(file_path):
+        file_object = self.filesystem.GetObjectFromNormalizedPath(real_path)
+      closefd = True
+
+    if file_object:
+      if ((need_read and not file_object.st_mode & PERM_READ) or
+          (need_write and not file_object.st_mode & PERM_WRITE)):
+        raise IOError(errno.EACCES, 'Permission denied', file_path)
+      if need_write:
+        file_object.st_ctime = int(time.time())
+        if truncate:
+          file_object.SetContents('')
+    else:
+      if must_exist:
+        raise IOError(errno.ENOENT, 'No such file or directory', file_path)
+      file_object = self.filesystem.CreateFile(
+          real_path, create_missing_dirs=False, apply_umask=True)
+
+    if file_object.st_mode & stat.S_IFDIR:
+      raise IOError(errno.EISDIR, 'Fake file object: is a directory', file_path)
+
+    class FakeFileWrapper(object):
+      """Wrapper for a StringIO object for use by a FakeFile object.
+
+      If the wrapper has any data written to it, it will propagate to
+      the FakeFile object on close() or flush().
+      """
+      if sys.version_info < (3, 0):
+        _OPERATION_ERROR = IOError
+      else:
+        _OPERATION_ERROR = io.UnsupportedOperation
+
+      def __init__(self, file_object, update=False, read=False, append=False,
+                   delete_on_close=False, filesystem=None, newline=None,
+                   binary=True, closefd=True):
+        self._file_object = file_object
+        self._append = append
+        self._read = read
+        self._update = update
+        self._closefd = closefd
+        self._file_epoch = file_object.epoch
+        contents = file_object.contents
+        newline_arg = {} if binary else {'newline': newline}
+        io_class = io.StringIO
+        # For Python 3, files opened as binary only read/write byte contents.
+        if sys.version_info >= (3, 0) and binary:
+          io_class = io.BytesIO
+          if contents and isinstance(contents, str):
+            contents = bytes(contents, 'ascii')
+        if contents:
+          if update:
+            self._io = io_class(**newline_arg)
+            self._io.write(contents)
+            if not append:
+              self._io.seek(0)
+            else:
+              self._read_whence = 0
+              if read:
+                self._read_seek = 0
+              else:
+                self._read_seek = self._io.tell()
+          else:
+            self._io = io_class(contents, **newline_arg)
+        else:
+          self._io = io_class(**newline_arg)
+          self._read_whence = 0
+          self._read_seek = 0
+        if delete_on_close:
+          assert filesystem, 'delete_on_close=True requires filesystem='
+        self._filesystem = filesystem
+        self._delete_on_close = delete_on_close
+        # override, don't modify FakeFile.name, as FakeFilesystem expects
+        # it to be the file name only, no directories.
+        self.name = file_object.opened_as
+
+      def __enter__(self):
+        """To support usage of this fake file with the 'with' statement."""
+        return self
+
+      def __exit__(self, type, value, traceback):  # pylint: disable-msg=W0622
+        """To support usage of this fake file with the 'with' statement."""
+        self.close()
+
+      def GetObject(self):
+        """Returns FakeFile object that is wrapped by current class."""
+        return self._file_object
+
+      def fileno(self):
+        """Returns file descriptor of file object."""
+        return self.filedes
+
+      def close(self):
+        """File close."""
+        if self._update:
+          self._file_object.SetContents(self._io.getvalue())
+        if self._closefd:
+          self._filesystem.CloseOpenFile(self)
+        if self._delete_on_close:
+          self._filesystem.RemoveObject(self.name)
+
+      def flush(self):
+        """Flush file contents to 'disk'."""
+        if self._update:
+          self._file_object.SetContents(self._io.getvalue())
+          self._file_epoch = self._file_object.epoch
+
+      def seek(self, offset, whence=0):
+        """Move read/write pointer in 'file'."""
+        if not self._append:
+          self._io.seek(offset, whence)
+        else:
+          self._read_seek = offset
+          self._read_whence = whence
+
+      def tell(self):
+        """Return the file's current position.
+
+        Returns:
+          int, file's current position in bytes.
+        """
+        if not self._append:
+          return self._io.tell()
+        if self._read_whence:
+          write_seek = self._io.tell()
+          self._io.seek(self._read_seek, self._read_whence)
+          self._read_seek = self._io.tell()
+          self._read_whence = 0
+          self._io.seek(write_seek)
+        return self._read_seek
+
+      def _UpdateStringIO(self):
+        """Updates the StringIO with changes to the file object contents."""
+        if self._file_epoch == self._file_object.epoch:
+          return
+        whence = self._io.tell()
+        self._io.seek(0)
+        self._io.truncate()
+        self._io.write(self._file_object.contents)
+        self._io.seek(whence)
+        self._file_epoch = self._file_object.epoch
+
+      def _ReadWrappers(self, name):
+        """Wrap a StringIO attribute in a read wrapper.
+
+        Returns a read_wrapper which tracks our own read pointer since the
+        StringIO object has no concept of a different read and write pointer.
+
+        Args:
+          name: the name StringIO attribute to wrap.  Should be a read call.
+
+        Returns:
+          either a read_error or read_wrapper function.
+        """
+        io_attr = getattr(self._io, name)
+
+        def read_wrapper(*args, **kwargs):
+          """Wrap all read calls to the StringIO Object.
+
+          We do this to track the read pointer separate from the write
+          pointer.  Anything that wants to read from the StringIO object
+          while we're in append mode goes through this.
+
+          Args:
+            *args: pass through args
+            **kwargs: pass through kwargs
+          Returns:
+            Wrapped StringIO object method
+          """
+          self._io.seek(self._read_seek, self._read_whence)
+          ret_value = io_attr(*args, **kwargs)
+          self._read_seek = self._io.tell()
+          self._read_whence = 0
+          self._io.seek(0, 2)
+          return ret_value
+        return read_wrapper
+
+      def _OtherWrapper(self, name):
+        """Wrap a StringIO attribute in an other_wrapper.
+
+        Args:
+          name: the name of the StringIO attribute to wrap.
+
+        Returns:
+          other_wrapper which is described below.
+        """
+        io_attr = getattr(self._io, name)
+
+        def other_wrapper(*args, **kwargs):
+          """Wrap all other calls to the StringIO Object.
+
+          We do this to track changes to the write pointer.  Anything that
+          moves the write pointer in a file open for appending should move
+          the read pointer as well.
+
+          Args:
+            *args: pass through args
+            **kwargs: pass through kwargs
+          Returns:
+            Wrapped StringIO object method
+          """
+          write_seek = self._io.tell()
+          ret_value = io_attr(*args, **kwargs)
+          if write_seek != self._io.tell():
+            self._read_seek = self._io.tell()
+            self._read_whence = 0
+            self._file_object.st_size += (self._read_seek - write_seek)
+          return ret_value
+        return other_wrapper
+
+      def Size(self):
+        return self._file_object.st_size
+
+      def __getattr__(self, name):
+        if self._file_object.IsLargeFile():
+          raise FakeLargeFileIoException(file_path)
+
+        # errors on called method vs. open mode
+        if not self._read and name.startswith('read'):
+          def read_error(*args, **kwargs):
+            """Throw an error unless the argument is zero."""
+            if args and args[0] == 0:
+              return ''
+            raise self._OPERATION_ERROR('File is not open for reading.')
+          return read_error
+        if not self._update and (name.startswith('write')
+                                 or name == 'truncate'):
+          def write_error(*args, **kwargs):
+            """Throw an error."""
+            raise self._OPERATION_ERROR('File is not open for writing.')
+          return write_error
+
+        if name.startswith('read'):
+          self._UpdateStringIO()
+        if self._append:
+          if name.startswith('read'):
+            return self._ReadWrappers(name)
+          else:
+            return self._OtherWrapper(name)
+        return getattr(self._io, name)
+
+      def __iter__(self):
+        if not self._read:
+          raise self._OPERATION_ERROR('File is not open for reading')
+        return self._io.__iter__()
+
+    # if you print obj.name, the argument to open() must be printed. Not the
+    # abspath, not the filename, but the actual argument.
+    file_object.opened_as = file_path
+
+    fakefile = FakeFileWrapper(file_object,
+                               update=need_write,
+                               read=need_read,
+                               append=append,
+                               delete_on_close=self._delete_on_close,
+                               filesystem=self.filesystem,
+                               newline=newline,
+                               binary=binary,
+                               closefd=closefd)
+    if filedes is not None:
+      fakefile.filedes = filedes
+    else:
+      fakefile.filedes = self.filesystem.AddOpenFile(fakefile)
+    return fakefile
+ 
+
+def _RunDoctest():
+  # pylint: disable-msg=C6204
+  import doctest
+  import fake_filesystem  # pylint: disable-msg=W0406
+  return doctest.testmod(fake_filesystem)
+
+
+if __name__ == '__main__':
+  _RunDoctest()