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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 available_configuration_files(self):
 """A list of strings with the absolute pathnames of the available configuration files."""

        known_files = [GLOBAL_CONFIG, LOCAL_CONFIG, self.environment.get('PIP_ACCEL_CONFIG')]
        absolute_paths = [parse_path(pathname) for pathname in known_files if pathname]
        return [pathname for pathname in absolute_paths if os.path.isfile(pathname)]