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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 walk(self, top, topdown=True, onerror=None, followlinks=False):
 """Perform a walk operation over the fake filesystem. Args: top: The 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. followlinks: If `True`, symbolic links are followed. Yields: (path, directories, nondirectories) for top and each of its subdirectories. See the documentation for the builtin os module for further details. """

        return walk(self.filesystem, top, topdown, onerror, followlinks)