[Python-Dev] PEP 572: Assignment Expressions (original) (raw)

Steven D'Aprano steve at pearwood.info
Tue May 1 03:00:53 EDT 2018

On Tue, May 01, 2018 at 11:04:55AM +1000, Chris Angelico wrote:

To be fair, I don't see many people replacing "x = 1" with "for x in [1]: pass". Even though it IS going to have the same effect. :-)

Aside from the pass, that is precisely one of the current work-arounds for lack of binding-expressions inside comprehensions:

# inefficient, and wrong when f(x) has side-effects
[f(x) for x in iterable if f(x) > 1]

# what we'd like
[y for x in iterable if (y := f(x)) > 1]

# a work-around
[y for x in iterable for y in [f(x)] if y > 1]

I think that's even in your PEP, isn't it?

-- Steve

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