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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 recall_checksum(self, cache_file):
 """ Get the checksum of the input used to generate a binary distribution archive. :param cache_file: The pathname of the binary distribution archive (a string). :returns: The checksum (a string) or :data:`None` (when no checksum is available). """

        # EAFP instead of LBYL because of concurrency between pip-accel
        # processes (https://docs.python.org/2/glossary.html#term-lbyl).
        checksum_file = '%s.txt' % cache_file
        try:
            with open(checksum_file) as handle:
                contents = handle.read()
            return contents.strip()
        except IOError as e:
            if e.errno == errno.ENOENT:
                # Gracefully handle missing checksum files.
                return None
            else:
                # Don't swallow exceptions we don't expect!
                raise