def write_signatures(self, signatures):
self.fileobj.seek(self.signature_offset)<EOL>sig_entries = [dict(algorithm_id=id_,<EOL>size=len(sig),<EOL>signature=sig)<EOL>for (id_, sig) in signatures]<EOL>sigs = sigs_header.build(dict(<EOL>filesize=self.filesize,<EOL>count=len(signatures),<EOL>sigs=sig_entries,<EOL>))<EOL>self.fileobj.write(sigs)<EOL>signatures_len = len(sigs)<EOL>self.additional_offset = self.signature_offset + signatures_len<EOL>if not self.additional_offset == self.fileobj.tell():  <EOL><INDENT>raise IOError('<STR_LIT>')<EOL><DEDENT>
Write signature data to the MAR file.

        Args:
            signatures (list): list of signature tuples of the form
                (algorithm_id, signature_data)