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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 GetMountPoint(self, path=None):
 """Walk back from the path to find the mount point. Args: path: a Unicode string containing the path or None. If path is None the value in self.path is used. Returns: path string of the mount point """

    path = os.path.abspath(
        client_utils.CanonicalPathToLocalPath(path or self.path))

    while not os.path.ismount(path):
      path = os.path.dirname(path)

    return path