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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 from_python_file( cls, python_file, lambdas_path, json_filename: str, stem: str ):
 """Builds GrFN object from Python file."""

        with open(python_file, "r") as f:
            pySrc = f.read()
        return cls.from_python_src(pySrc, lambdas_path, json_filename, stem)