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

append_sequence(sequence, blank_single_chain=True)
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.

If only one chain is generated, and blank_single_chain is True (the default), it is given a blank chain ID. Otherwise, the chains are labeled 'A', 'B', 'C' and so on.
Example: See model.build_sequence() command.