I would like to know if is Python on every G/L distribution preinstalled or not. And why is it so popular on GNU/Linux and not so much on Windows?
Well python does not come on ALL GNU/Linux distros but is present on most of the popular Linux home user distributions (Ubuntu and Fedora Core for example), possibly because most of the application of Gnome desktop environment and KDE use python 2.5+ (not python 3 yet) interpreters. Since python is almost integrated onto the system/environment from the start, linux users feel easy to program in python. But this is a subjective opinion, as java is still equally popular, if not more, on linux distributions.
Similarly, windows (vista/7) comes prepacked with .net framework, with awesome support for C#, and on Mac OSX objective-C is dominant for most os integrated apps; users just tend to program in languages they deem more "native" to the development environment they are using/targeting.
No, Python is not pre-installed neither installed on every Linux distro.
来源：https://stackoverflow.com/questions/6786693/is-python-on-every-gnu-linux-distribution