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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 get_checksum(self, encoder=base64.b64encode, hasher=hashlib.sha256):
 """Return the b64 encoded sha256 checksum of the archive."""

        assert self._closed, "Archive not closed"
        with open(self._temp_archive_file.name, 'rb') as fh:
            return encoder(checksum(fh, hasher())).decode('ascii')