[Python-Dev] Naming comprehension syntax [was Re: Informal educator feedback on PEP 572 ...]

Chris Barker chris.barker at noaa.gov
Sun Jul 15 12:58:27 EDT 2018

Thanks Nick,

I'll adopt this approach when I update my teaching materials.

If I think of it, I"ll post here when I do that


On Sun, Jul 15, 2018 at 12:21 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 13 July 2018 at 15:30, Chris Barker via Python-Dev
> <python-dev at python.org> wrote:
> > On Mon, Jul 9, 2018 at 3:18 PM, Guido van Rossum <guido at python.org>
> wrote:
> >>
> >> Definitely docs first. And we should keep references to generator
> >> expressions too, if only to explain that they've been renamed.
> >>
> >> Perhaps someone should try it out in a 3rd party tutorial to see how it
> >> goes?
> >
> >
> > I'm not sure what "trying it out in a tutorial" would look like.
> >
> > I try to be pretty clear about terminology when I teach newbies -- so I
> > don't want to tell anyone this new thing is called a "generator
> > comprehension" if they aren't going to see that term anywhere else.
> Nina Zakharenko made the "they're officially called generator
> expressions, but I find it more helpful to think of them as generator
> comprehensions" observation in her PyCon 2018 presentation on "Elegant
> Solutions for Everyday Python Problems":
> https://www.slideshare.net/nnja/elegant-solutions-for-
> everyday-python-problems-pycon-2018/27
> The article from Ned Batchelder mentioned in that slide is this one,
> which goes through the history of Raymond originally proposing the
> notion as generator comprehensions, them getting changed to generator
> expressions during the PEP 289 discussions, and then asking if it
> might be worth going back to the originally suggested name:
> https://nedbatchelder.com/blog/201605/generator_comprehensions.html
> And then in PEP 572, it was found that being able to group all 4
> constructs (list/set/dict comps + generator expressions) under a
> single term was a genuinely useful shorthand:
> https://www.python.org/dev/peps/pep-0572/#scope-of-the-target
> So trying out the terminology in a tutorial context would be to do
> something similar to what Nina did in her talk: introduce the notion
> of list/set/dict/generator comprehensions, and then make a side note
> that the latter are officially referred to as "generator expressions".
> This wouldn't be the first time that terminology has differed between
> Python-as-commonly-taught and Python-as-formally-defined, as I've yet
> to hear anyone refer to container displays outside a language design
> discussion - everyone else calls them container literals (or, more
> typically, a literal for the specific builtin container type being
> discussed).
> In this case, though, we'd be considering eventually changing the
> language reference as well, and perhaps even some day the AST node
> name (from GeneratorExp to GeneratorComp).
> We wouldn't need to change anything in the grammar definition (since
> that already shares the comp_for and comp_if syntax definitions
> between container comprehensions and generator expressions), or the
> AST node structure (since GeneratorExp already uses a "comprehensions"
> attribute, the same as the ListComp/SetComp/DictComp nodes).
> Cheers,
> Nick.
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia


Christopher Barker, Ph.D.

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