[Python-ideas] Long Live PEP 3150 (was: Re: Statement local functions and classes (aka PEP 3150 is dead, say 'Hi!' to PEP 403))

[Paul Moore]

On 16 October 2011 08:16, Nick Coghlan <ncoghlan at gmail.com> wrote:
> We may also decide to eliminate the "new scope" implications for
> 'given' statements entirely and focus solely on the "out of order
> execution" aspect. That would not only simplify the implementation,
> but also make for a cleaner extension to the compound statement
> headers.

FWIW, I did a quick review of some of my own code where I expected the
given clause to be helpful (relatively mathematical code computing
continued fractions - lots of complex expressions with subexpressions
that can be factored out using throwaway names, and very few of the
subexpressions are meaningful enough by themselves to make coming up
with helpful names really viable).

I was surprised to find that the in-line code, using a lot of x's and
y's, was readable enough that I could find little use for the given
clause.

If the "new scope" semantics is included, I might have got some small
benefits from being able to reuse x and y all over the place safe in
the assurance that a typo wouldn't cause me to silently pick up the
wrong value. But even that is stretching for benefits.

I still like the idea in principle, but I'm no longer sure it's as
useful in practice as I'd expected. A really good use case would help
a lot (Nick's argparse example is a start, but I'm nervous about the
idea of writing an API that relies on out of order evaluation to be
readable).

Paul.