Alignment.append_sequence() — add a sequence from one-letter codes

append_sequence(sequence, blank_single_chain=False)
This builds a new sequence from the provided one-letter codes, and adds it to the end of the alignment. You can also use '-' and '/' characters in this sequence to add gaps and chain breaks.

By default, the newly created chains are labeled 'A', 'B', 'C' and so on. However, if only one chain is generated, and blank_single_chain is set True, it is given a blank chain ID.
Example: See Model.build_sequence() command.