sets up a command to be executed upon entry into the specified frame of the movie. These commands are usually created by a PyMOL utility program (such as util.mrock). Command can actually contain several commands separated by semicolons ';'
cmd.mdo( int frame, string command )
//Show waters within 4 Angstroms around the first residue from a 15 frame simulation trajectory
load structure.pdb
load_traj structure.dcd, structure, start=1, stop=15
mset 1 -15
for a in range(1,16): cmd.mdo(a,"hide sphere; select waters, (structure & i. 1 around 4) & resn HOH, state="+str(a)+"; show sphere, waters")