The Colt .357's heritage originally was the Colt Official Police.
The frame is a ".41" in size and the Official Police handled
the .38/44 loads of the 1930s which were a .38 round with a
158 grain bullet propelled at 1,100 feet a second.
Smith's comparable gun to the Official Police in handling the
hotter .38s was, of course, the Smith .38/44 HD on the N-frame.
Then Smith in 1935 created the .357 designation for its N frames. The .357 in some configurations was a bit hotter
than the .38/44 and the .357 had a slightly longer casing.
And yes, the Python really is an extension of the Official Police
and thus the Colt .357.
By 1955 metallurgy for handguns was improving and so
Smith issued the Model 19 but it was still on the lighter
K-frame.
The Model 19 is a superb revolver and though it's not fragile,
it still is not quite as robust as the Colt .357s. So Smith
in 1980 issued the L-frame, essentially the same sized frame
as the Colt Official Police/Colt .357/Python.
Just as an aside, for those who love the Python action, and stick with .38 Specials any way, consider the Official Police. They
are not only available, having been made into the 1960s I believe, but are offered at fairly reasonable prices, more in the
sub $1,000 area and can be had for a lot less than that.
I think metallurgical technology is probably very important so if you wish to "magnatize" any
of the older guns it's probably best to stick with post 1955 models.