Back about a dozen years ago when Colt was again looking for cash, a bunch of "spare" parts hit the gun show circuit. I remember seeing a few Colt revolver barrels and Colt 1911 pistol slides with no markings. I don't think these parts were meant for direct retail sale, but when you need cash just move that inventory. So I guess the answer to your question is "Maybe" the barrel is real. As for value, I have no clue. I'm sure some would covet it while others would treat it as The Spawn of Satan.

 

Colt normally did not sell any revolvers, including the Python without barrel stamps.
EXCEPT, it appears Colt did sell a very few Pythons with no markings at all so they could be engraved.
We've seen a few here on the forum, and they appear to have not have shipped with a finish, and were likely a special order from the Custom Shop.

It's at least possible a Python slipped out of the factory with a factory defect of no barrel stamps, but that would be extremely rare.

Bottom line, the most likely explanation is that someone picked up one of the above mentioned loose and unmarked barrels and used to to re-barrel the gun.
OR, it's possible the gun was way over polished during a ham-handed refinish and the marks were buffed off.

In the case of a engravers gun or a factory defect, the value would probably be less.
In the case of a crude refinish or a re-barrel, the value would plunge steeply.

In short, this is one of those guns you'd approach very, very carefully, with the probability that it's not worth the asking price and never will be worth as much as a standard gun.