Context-aware return

Steven D'Aprano steve at
Thu Sep 10 19:54:14 CEST 2015

I have a function which is intended for use at the interactive interpreter,
but may sometimes be used non-interactively. I wish to change it's output
depending on the context of how it is being called.

If the function is being called as if it were a procedure or command, that
is the return result is just ignored, I want to return one thing. But if it
is being called where the return result goes somewhere, I want to return
something else. Most importantly, I don't want to pass a flag to the
function myself, I want the function to know its own context.

I don't mind if it is CPython only, or if it is a bit expensive.


def func():
    if procedure:  # FIXME what goes here???
        return "Awesome"
        return 999

Now I can do this:

x = func()
assert x == 999

L = [1, 2, func(), 4]
assert L[2] == 999

# interactive interpreter prints "Awesome"

Is such a thing possible, and if so, how would I do it?

If I did this thing, would people follow me down the street booing and
jeering and throwing things at me?


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