“pop” provides a mechanism of iterating through an atom selection atom by atom, where each atom is sequentially assigned to the named selection.

pop name, source

select src, name ca 

python 
while cmd.pop("tmp","src"): 
    cmd.zoom("tmp",2, animate=1) 
    for a in range(30): 
       cmd.refresh() 
       time.sleep(0.05) 
python end 

cmd.pop | commands