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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 generate_filename(self, requirement):
 """ Generate a distribution archive filename for a package. :param requirement: A :class:`.Requirement` object. :returns: The filename of the distribution archive (a string) including a single leading directory component to indicate the cache format revision. """

        return FILENAME_PATTERN % (self.config.cache_format_revision,
                                   requirement.name, requirement.version,
                                   get_python_version())