It’s a lot easier in C++ or Java. In C++, you make the virtual calls to some base class, and all you need to demonstrate is that only one concrete class is being used at that place. For example, you might see a List<T> in Java, and then the JIT compiler figures out that the field is always assigned = new ArrayList<T>(), which allows it to devirtualize.

In Python, the types are way more general. Basically, every method call is being made to “object”. Every field has a value of type “object”. This makes it much more difficult for the compiler to devirtualize anything. It might be much harder to track which code assigns values to a particular field, because objects can easily escape to obscure parts of your codebase and be modified without knowing their type at all.

This happens even if you write very boring, Java-like code in Python.