One more:
The Python didn't change much at all, and statements about "Generations" of Pythons you sometimes hear are not really valid, since the few changes were so minor.
The very early Pythons of the 1950's had a slightly different barrel rib and front sight. This was mostly due to the Colt Accro sight of that era being different then the later Accro. When Colt changed the Accro to the "humped" version to give more elevation adjustment the Python top rib and sight were necessarily changed.
The VERY early Accro sight had a rounded end on the sight leaf, which was changed within a couple of years to a squared off leaf.
The 50's Pythons had a hollow barrel lug, changed to a solid lug later.
Other than that, the only changes were the grips, finishes and the stamping of the word "Elite" on the very late 1990's Pythons.
Standard finishes were Royal Blue, Bright Nickel, satin electroless nickel known as "Royal Coltguard", satin stainless, and bright polish stainless.
Here's the changes to the standard Colt Accro rear sight.
Early Accro used during the 1950's. Note the rounded front sight leaf and the simpler elevation screw assembly.
Early Accro in place.
Later Accro. Note the "hump" in the sight leaf to give more elevation, the squared sight leaf and the more complicated elevation screw assembly. This sight was used on virtually all Colt pistols that had adjustable sights. This one is the early version with the "U" shaped notch in the sight base. Later versions changed to a rectangular notch to allow more windage adjustment.
Early Accro with square front sight leaf. This quickly replaced the original round leaf Accro within a couple of years.
