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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 checksum(self, chunk_size=None, progress_callback=None, **kwargs):
 """Compute checksum of file."""

        fp = self.open(mode='rb')
        try:
            value = self._compute_checksum(
                fp, size=self._size, chunk_size=None,
                progress_callback=progress_callback)
        except StorageError:
            raise
        finally:
            fp.close()
        return value