On Wed, Nov 18, 2020 at 7:45 PM Brett Cannon <br...@python.org> wrote:
> > > On Tue, Nov 17, 2020 at 10:16 PM Greg Ewing <greg.ew...@canterbury.ac.nz> > wrote: > >> On 18/11/20 4:36 pm, Larry Hastings wrote: >> > >> > But, >> > the thinking went, you'd never want to examine the last value from a >> > list generator, so it was more convenient if it behaved as if it had >> its >> > own scope. >> >> List comprehensions used to leak, but apparently that was considered >> surprising by enough people that it was changed. >> >> Generator expressions are a bit different -- the only sane way to >> implement them was to make the body implicitly a separate function, >> and non-leaking behaviour naturally fell out of that. Making them >> leak would have taken extra work just to get something that nobody >> really had a good use case for. >> >> The desire to make list comprehensions and generator expressions >> behave consistently may have contributed to the decision to change >> list comprehensions to be non-leaking. >> > > It did if I remember correctly. > > For me, generator expressions are small functions like you say (see, > people did get the equivalent of multi-line lambdas, just in a very > specific format 😉), and all the comprehensions are just passing a > generator expression to the appropriate constructor, e.g. list(), set(), > and dict(). In that regard the scoping is consistent to me. > > -Brett > > If match were to create a scope, would making names in that scope nonlocal by default work? (Obvs we'd then need a local declaration, but given global's long-standing presence in the language and the more recent addition of nonlocal it seems like a fairly natural extension).
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