The Colt Python is notorious for developing some loose internal screws.

Take a look at the right side of the frame just behind the cylinder shield.
See if it looks like one of the screw ends that protrude there seems "depressed" or not as high as others. What may have happened is that
the screw that controls the armature to the cylinder stop bar has worked loose. It simply needs tightening but the gun must be opened, i.e. the
side plate on the left side must be removed. The most critical part of doing this is not to let the thumb release for the cylinder fly loose and a tiny coiled-flat spring goes into space. Be sure to ease the thumb release out carefully. Once the side plate is off, it's not so complicated.

Get a schematic and you'll better understand things. However, it never hurts to locate a good or at least decent gunsmith to do the work.