Python is not a very dynamic language in the sense that you actually can't change a lot of stuff (and a number of the things you can change just segfault CPython). I think JS is more dynamic, for example. Or Ruby.
You've piqued my interest, though: can you give me an example of those things that you can't change or that break CPython?
>>> import gc
>>> 'foo'.lower()
>>> gc.get_referents(str.__dict__)[0]['lower'] = str.upper
>>> 'foo'.lower()
segmentation fault (core dumped) python
A talk in this direction is https://www.youtube.com/watch?v=qCGofLIzX6g