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alter changes one or more atomic properties over a selection using the python evaluator with a separate name space for each atom. The symbols defined in the name space, which are are explained in Iterate are:

name, resn, resi, chain, alt, elem, q, b, segi,
type (ATOM,HETATM), partial_charge, formal_charge,
text_type, numeric_type, ID, vdw

All strings must be explicitly quoted. This operation typically takes several seconds per thousand atoms altered.

WARNING: You should always issue a sort command on an object after modifying any property which might affect canonical atom ordering (names, chains, etc.). Failure to do so will confound subsequent "create" and "byres" operations.


alter (selection),expression


Change chain label and residue index

 alter (chain A),chain='B'
 alter (all),resi=str(int(resi)+100)

Change van der Waals radius of a given atom

alter (name P), vdw=1.90

Note that is if dots, spheres, mesh or surface representation is used. You have to refresh the view with


Renumber the amino acids in a protein, so that it starts from 0 instead of its offset as defined in the structure file

# The first residue in the structure file for 1cll is 4.  To change this to 0, maybe to match scripts
# outputted from other programs, just remove the offset of 4 from each atom
alter 1cll, resi=str(int(resi)-4)
# refresh (turn on seq_view to see what this command does).

Change the b values of all atoms to the distance of the atoms to a reference point

# reference point
# calculate distance values between the reference point and all the atoms
alldist = []
iterate_state 1, yourstruc, alldist.append(((x-x0)**2.0+(y-y0)**2.0+(z-z0)**2.0)**0.5)
# assign distance values to b-factors 
di = iter(alldist)
alter yourstruc,
# visualize the distances
spectrum b, rainbow, yourstruc

Copy (transfer) the color from one object to another

stored.colors = {}
iterate obj1, stored.colors[chain,resi,name] = color
alter obj2, color = stored.colors.get((chain,resi,name), color)


cmd.alter(string selection, string expression, int quiet=1, dict space=None)

As explained before, all strings must be explicitly quoted. For example to change all HETATM records to ATOM you should do:

cmd.alter('all', 'type="ATOM"')


Alter_State, iterate, Iterate_State, sort