Securing a future for anonymous functions in Python

[Tim Peters]

...

[Anna]
>> BTW - I am *quite* happy with the proposal for "where:" syntax - I
>> think it handles the problems I have with lambda quite handily.

[Steve Holden]
> Whereas I find it to be an excrescence, proving (I suppose) that one
> man's meat is another person's poison, or something.

I've been waiting for someone to mention this, but looks like nobody
will, so I'm elected.  Modern functional languages generally have two
forms of local-name definition, following common mathematical
conventions.  "where" was discussed here.  The other is "let/in", and
seems a more natural fit to Python's spelling of block structure:

    let:
        suite
    in:
        suite

There's no restriction to expressions here.  I suppose that, like the
body of a class, the `let` suite is executed starting with a
conceptually empty local namespace, and whatever the suite binds to a
local name becomes a temporary binding in the `in` suite (like
whatever a class body binds to local names becomes the initial value
of the class __dict__).  So, e.g.,

    i = i1 = 3
    let:
        i1 = i+1
        from math import sqrt
    in:
        print i1, sqrt(i1)
    print i1,
    print sqrt(i1)

would print

    4 2
    3

and then blow up with a NameError.

LIke it or not, it doesn't seem as strained as trying to pile more
gimmicks on Python expressions.