from pymol import cmd,stored
def average_b(selection):
	stored.tempfactor=0
	stored.atomnumber=0
	cmd.iterate(selection,"stored.tempfactor=stored.tempfactor+b")
	cmd.iterate(selection,"stored.atomnumber=stored.atomnumber+1")
	print "Your selection: ", selection
	print "sum of B factors: ", stored.tempfactor
	print "number of atoms: ",stored.atomnumber
	averagetempfactor=stored.tempfactor/stored.atomnumber
	print "average B of '", selection,"': ", averagetempfactor
cmd.extend("average_b",average_b)