Holy shit, you typed "python" in a console window so the OS looked for an existing install, didn't find one, so it tried to help you! How evil and awful! Burn M$$$$ down! unknown command 'python' is the only proper way to respond!
And for every new generation of know-nothings that grows up to replace the veterans of wars long past, all the old battles will need to be re-fought... Sigh. I'm too old for this shit; geroffmylawn.
That’s not what happened. Python was installed and on the PATH, it just refused to use it as long as that alias check box was turned on in system settings.
