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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 add_variables_from_directory(self, directory):
 """ Recursively explores a directory, and adds all OpenFisca variables found there to the tax and benefit system. """

        py_files = glob.glob(path.join(directory, "*.py"))
        for py_file in py_files:
            self.add_variables_from_file(py_file)
        subdirectories = glob.glob(path.join(directory, "*/"))
        for subdirectory in subdirectories:
            self.add_variables_from_directory(subdirectory)