Draft pull request to illustrate#4922.

• TheCifSeqresIterator (cif-seqres) uses "label" IDs (_pdbx_poly_seq_scheme.asym_id), which are assigned by the PDB, always start at "A" and move through the alphabet one letter at a time.

• TheCifAtomIterator (cif-atom) uses "author" IDs, which are arbitrarily assigned by the structure authors (this is what you get in traditional fixed-width PDB files).

I agree that this mismatch is probably a bug, though it would be a backwards incompatible change to fix it. If you don't care about the author IDs, and you just need the chain IDs of the sequence fromcif-seqres to match the chain IDs of the atoms parsed byMMCIFParser, you could passauth_chains=False toMMCIFParser to use label IDs in the structure as well.

To fix this, theCifSeqresIterator could be modified to use author IDs by reading
_pdbx_poly_seq_scheme.pdb_strand_id. Or theCifAtomIterator could passauth_chains=False toMMCIFParser to use label IDs everywhere.

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Closes #...