def __getitem__(self, seq_name):
try:<EOL><INDENT>return self.sequences[seq_name]<EOL><DEDENT>except KeyError:<EOL><INDENT>raise InvalidSequenceError("<STR_LIT>" +<EOL>str(seq_name) + "<STR_LIT>" +<EOL>"<STR_LIT:U+002CU+0020>".join(self.sequences.keys()))<EOL><DEDENT>
:return: the sequence with the given name in this alignment.