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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 read_envvar_file(name, extension):
 """ Read values from a file provided as a environment variable ``NAME_CONFIG_FILE``. :param name: environment variable prefix to look for (without the ``_CONFIG_FILE``) :param extension: *(unused)* :return: a `.Configuration`, possibly `.NotConfigured` """

    envvar_file = environ.get('{}_config_file'.format(name).upper())
    if envvar_file:
        # envvar set, load value as file
        return loadf(envvar_file)
    else:
        # envvar not set, return an empty source
        return NotConfigured