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

Glenn Linderman v+python at g.nevcal.com
Tue Apr 17 12:23:14 EDT 2018

On 4/17/2018 12:46 AM, Chris Angelico wrote:

gen = (x for x in rage(10)) # NameError gen = (x for x in 10) # TypeError (not iterable) gen = (x for x in range(1/0)) # Exception raised during evaluation

This brings such generator expressions in line with a simple translation to function form:: def (): for x in rage(10): yield x gen = () # No exception yet tng = next(gen) # NameError Detecting these errors more quickly is nontrivial. It is, however, the exact same problem as generator functions currently suffer from, and this proposal brings the genexp in line with the most natural longhand form.

Open questions ============== Can the outermost iterable still be evaluated early? ---------------------------------------------------- As of Python 3.7, the outermost iterable in a genexp is evaluated early, and the result passed to the implicit function as an argument. With PEP 572, this would no longer be the case. Can we still, somehow, evaluate it before moving on? One possible implementation would be:: gen = (x for x in rage(10)) # translates to def (): iterable = iter(rage(10)) yield None for x in iterable: yield x gen = () next(gen)

I think "rage" is supposed to be "range" in four places in the quoted block. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20180417/af56c615/attachment.html>

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