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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def GetFileSystem(self, path_spec):
 """Retrieves a file system object defined by path specification. Args: path_spec (PathSpec):
 path specification. Returns: FileSystem: a file system object or None if not cached. """

    identifier = self._GetFileSystemCacheIdentifier(path_spec)
    return self._file_system_cache.GetObject(identifier)