Is there a situation where Python ever passes by value? Like you can sort of pretend for primitive types but I can't think of case where it's actually value.
(It's surprisingly difficult to implement a rigorous way to detect this vs compile-time constant evaluation though; note that identical objects of certain types are pooled already when generating/loading bytecode files. I don't think any current implementation is smart enough to optimize the following though)
$ python3 -c 'o = object(); print(id(o) is id(o))'
False
$ pypy3 -c 'o = object(); print(id(o) is id(o))'
True
$ jython -c 'o = object(); print(id(o) is id(o))'
True $ python -c "print(int('3') is int('3'))"
True
$ python -c "print(int('300') is int('300'))"
False