Chain.atom_file_and_code() — get suitable names for this chain

Given a model filename, this returns suitable atom_file and align_code values for this chain, for example for giving to Chain.write(). Path names are stripped, and duplicate chain IDs are handled.

For example, a model filename of /home/user/test.pdb may return test for atom_file and testA for align_code when called for the A chain.
Example: See Chain.filter() command.

Automatic builds 2017-07-19