Tail recursion to while iteration in 2 easy steps

[Alain Ketterlin]

Terry Reedy <tjreedy at udel.edu> writes:

> Part of the reason that Python does not do tail call optimization is
> that turning tail recursion into while iteration is almost trivial,
> once you know the secret of the two easy steps. Here it is.
>
> Assume that you have already done the work of turning a body recursive
> ('not tail recursive') form like
>
> def fact(n): return 1 if n <= 1 else n * fact(n-1)
>
> into a tail recursion like
[...]

How do know that either "<=" or "*" didn't rebind the name "fact" to
something else? I think that's the main reason why python cannot apply
any procedural optimization (even things like inlining are impossible,
or possible only under very conservative assumption, that make it
worthless).

-- Alain.

P/S: don't take me wrong; your explanation is excellent (and very useful
to python programmers). What I say is that it relies on assumptions that
do not apply to python.