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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 _ReadDefinitionFile(self, filename):
 """Reads a dtFabric definition file. Args: filename (str):
 name of the dtFabric definition file. Returns: dtfabric.DataTypeFabric: data type fabric which contains the data format data type maps of the data type definition, such as a structure, that can be mapped onto binary data or None if no filename is provided. """

    if not filename:
      return None

    path = os.path.join(self._DEFINITION_FILES_PATH, filename)
    with open(path, 'rb') as file_object:
      definition = file_object.read()

    return dtfabric_fabric.DataTypeFabric(yaml_definition=definition)