[PyMOL] measure angles in programming

[rainfieldcn <rai...@gm...>]

Hi all,
I generate two pseudoatoms "start_point" and "end_point" by 
center_of_mass.py. I load an object "tunnel" which has a sets of atoms 
in one chain.
I want to measure the angle from each atoms in "tunnel" to "end_point" 
to "start_point". at the same time, I want to print the B-factor of 
atoms in "tunnel".
To measure the angle, I programmed like this，but it doesn't work.
I guess it's because get_angle function needs some particular variable 
format.
By the way, how can I print the b factor of atom?
Thanks,
Lei

from pymol import cmd, stored
def vertical_distance( start_point, end_point, tunnel ):
centers = cmd.get_model(tunnel,1)
for a in centers.atom:
angle= cmd.get_angle(start_point, end_point,a)
print angle
return (start_point, end_point, tunnel)
cmd.extend( "vertical_distance", vertical_distance );