'Get a dependency graph for the function `func`.
:param func:    The Function object in CFG.function_manager.
:returns:       A networkx.DiGraph instance.'

def function_dependency_graph(self, func):

    if (self._function_data_dependencies is None):
        self._build_function_dependency_graphs()
    if (func in self._function_data_dependencies):
        return self._function_data_dependencies[func]
    return None
