[Python-Dev] Tricky way of of creating a generator via a comprehension expression (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Wed Nov 22 11:24:04 EST 2017

On Wed, 22 Nov 2017 17:08:14 +0100 Ivan Levkivskyi <levkivskyi at gmail.com> wrote:

On 22 November 2017 at 16:56, Yury Selivanov <yselivanov.ml at gmail.com> wrote:

> On Wed, Nov 22, 2017 at 10:10 AM, Ivan Levkivskyi <levkivskyi at gmail.com> > wrote: > > On 22 November 2017 at 15:47, Paul Moore <p.f.moore at gmail.com> wrote: > [...] > I'm all for prohibiting using 'yield' expression in generator > expressions or comprehensions. The semantics is way to hard to > understand and hence be of any value. > > Making 'await' a SyntaxError is absolutely not an option. Async > generator expressions are a shorthand syntax for defining asynchronous > generators (PEP 525), and it's already being used in the wild. > OK, makes sense, so it looks like we may have the following plan: - fix yield in comprehensions - update PEP 530 and docs re generator expressions vs comprehensions - make yield in generator expressions a SyntaxError

Given a comprehension (e.g. list comprehension) is expected to work nominally as constructor(generator expression) (e.g. list(generator expression)), I think both generator expressions and comprehensions should raise a SyntaxError.

(more exactly, they should first emit a SyntaxWarning and then raise a SyntaxError in a couple of versions)

Regards

Antoine.

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