human
I wrote the below code

    from Bio.PDB import PDBParser
    from Bio.SeqUtils import seq1
    def restype(residue):
        "Return    a    residue's    type    as    a    one-letter    code.\n\n                                Non-standard    residues    (e.g.    CSD,    ANP)    are    returned    as    'X'.\n                                "
        return seq1(residue.resname, custom_map=protein_letters_3to1)
    from Bio.File import UndoHandle
    undo_handle = UndoHandle(handle)
    firstline = undo_handle.peekline()
    if firstline.startswith('HEADER'):
        pdb_id = firstline[62:66]
    else:
        warnings.warn(("First    line    is    not    a    'HEADER'.
   can't    determine    PDB    ID.    Line:    %r" % firstline), BiopythonWarning)
        pdb_id = '????'
    struct = PDBParser().get_structure(pdb_id, undo_handle)
    model = struct[0]
    for (chn_id, chain) in sorted(model.child_dict.items()):
        residues = [res for res in chain.get_unpacked_list() if (seq1(res.get_resname().upper(), custom_map=protein_letters_3to1) != 'X')]
        if (not residues):
            continue
        gaps = []
        rnumbers = [r.id[1] for r in residues]
        for (i, rnum) in enumerate(rnumbers[:(-1)]):
            if (rnumbers[(i + 1)] != (rnum + 1)):
                gaps.append(((i + 1), rnum, rnumbers[(i + 1)]))
        if gaps:
            res_out = []
            prev_idx = 0
            for (i, pregap, postgap) in gaps:
                if (postgap > pregap):
                    gapsize = ((postgap - pregap) - 1)
                    res_out.extend((restype(x) for x in residues[prev_idx:i]))
                    prev_idx = i
                    res_out.append(('X' * gapsize))
                else:
                    warnings.warn('Ignoring    out-of-order    residues    after    a    gap', BiopythonWarning)
                    res_out.extend((restype(x) for x in residues[prev_idx:i]))
                    break
            else:
                res_out.extend((restype(x) for x in residues[prev_idx:]))
        else:
...

What's a good function header?
 Write me a Python program to determine    PDB    ID?
assistant
#Here is Python program to determine    PDB    ID.

def PdbAtomIterator(handle):