There are a number of command line shells available on iOS, right up to full blown programming environments in Python, Lua, C# and others. Pythonista is pretty mature, comes with a command line interpreter and you can get a very capable user created enhanced shell environment for it.
In the context of Python, don't forget Pyto! I use it lots for scripting tricky bits in the Shortcuts app in a real programming language. It has nice Shortcuts actions for "run this Python code" and "get the results of that code you ran earlier".
Same. It's way rougher around the edges than Pythonista is, but it's moving fast and adding nice support for new iOS features. For one example, from what I can tell x-callback-url is the only way to get stuff into Pythonista (and I haven't found a way to get stuff back out of it), but Pyto natively supports Shortcuts actions. There are lots of other things like that.
Pythonista is much more pleasant today for actually writing code in, though.
