It's not body replacement, it's function reference erasing. There is no way in Python to tell something has been replaced or not, since variables are dumb label

It's not body replacement, it's function reference erasing. There is no way in Python to tell something has been replaced or not, since variables are dumb labels and a reference is the same kind for any object. In fact, there is no particular difference between 2 objects in python. E.G: functions are objects, and any object can be called as a function. And it's just a reference to "something callable" in the namespace mapping (literally a dict in most implementations), which is mutable by definition Also a compiler flag would not help, since most users don't compile the python VM. Now, you could put a runtime flag, that list all stuff that are created for the first time in a namespace, and refuse to allow reassignment. It's possible, but it would break a LOT of things and prevent many patterns. The last attempt was to put guards, and to assume no replacement, but if a replacement occurs, then at this moment we revert locally this assumption. The process is refined at each iteration, but there is no turn-key solution as you seem to believe.