Hello Pymol Users

I am quite new to python and more specifically to PYTHON ,PYMOL interface hence I urgently need a help from you.

I simple need to calculate the RMSD between two pdb files and use that rmsd for further programming but somehow I can not figure how to do it

This is what I have written till now
[codes are in bold]

from pymol import cmd


This I believe should just load in the PDBs through PYMOL  [both these pdbs are in the same directory]

rms=cmd.fit(pdb  ???? )    so I do not know how to get the RMSD using this function ( I need for CA atoms only)

This is the only part where I am getting jammed . I only need the RMSD values between the structures(without any changes to the structures)

Can you advise me further on this one ?
Any help would be appreciated.