The Python Apprentice

Python return semantics

Python's return statement uses the same pass-by-object-reference semantics as function arguments. When you return an object from a function in Python, what you're really doing is passing an object reference back to the caller. If the caller assigns the return value to a reference, they are doing nothing more than assigning a new reference to the returned object. This uses the exact same semantics and mechanics that we saw with explicit reference assignment and argument passing.

We can demonstrate this by writing a function which simply returns its only argument:

>>> def f(d):...     return d...

If we create an object such as a list and pass it through this simple function, we see that it returns the very same object that ...