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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 AddDir(self, dirpath):
 """Adds a directory path as a source. Args: dirpath: a string representing a path to the directory. Returns: True if the directory is not an already existing source. """

    if dirpath not in self._dirs:
      self._dirs.add(dirpath)
      return True
    return False