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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_envvar(self, variable_name):
 """Load a configuration from an environment variable pointing to a configuration file. :param variable_name: name of the environment variable :return: bool. ``True`` if able to load config, ``False`` otherwise. """

        config_file = os.environ.get(variable_name)
        if not config_file:
            raise RuntimeError(
                "The environment variable %r is not set and "
                "thus configuration could not be loaded." % variable_name
            )
        return self.from_pyfile(config_file)