[BioPython] Atom serial number in Bio.PDB.PDBParser

[Michael Schmitt]

Hello.

Is there a way to get the atom serial numbers in a structure I retrieved in 
the following way:

from Bio.PDB.PDBParser import PDBParser
p= PDBParser(PERMISSIVE=1)
filename= 'testprotein.pdb'
s= p.get_structure(testid, filename)

The Atom objects have identifiers containing atom names, but I can't find the 
serial numbers.

Thanks for help.
Michael