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

Ivan Pozdeev vano at mail.mipt.ru
Fri Jul 6 20:33:30 EDT 2018

On 07.07.2018 2:58, Ivan Pozdeev via Python-Dev wrote:
> On 07.07.2018 2:31, Guido van Rossum wrote:
>> On Fri, Jul 6, 2018 at 4:19 PM Terry Reedy <tjreedy at udel.edu 
>> <mailto:tjreedy at udel.edu>> wrote:
>>     Since Guido, the first respondent, did not immediately shoot the
>>     idea
>>     down, I intend to flesh it out and make it more concrete.
>> Maybe I should have shot it down. The term is entrenched in multiple 
>> languages by now (e.g. 
>> https://en.wikipedia.org/wiki/List_comprehension). Regarding "list 
>> builder" one could argue that it would just add more confusion, since 
>> there's already an unrelated Builder Pattern 
>> (https://en.wikipedia.org/wiki/Builder_pattern) commonly used in 
>> Java. (Though I worry about the presence of a Python example in that 
>> Wikipedia page. :-)
> According to https://en.wikipedia.org/wiki/List_comprehension#History, 
> the term's known from at least 1977 and comes from such influential 
> languages as NPL, Miranda and Haskell. So it's not you to blame for it :-)
>> Also, "generator builder" is not much more expressive than "generator 
>> expression",
> "generator builder" is simply incorrect. The GE doesn't "build" 
> generators, it's a generator itself. It's a generator _and_ an 
> expression. What could be a more obvious name?
> This suggestion looks like coming from someone who hasn't quite 
> grasped generators yet.
>> and the key observation that led to this idea was that it's such a 
>> mouthful to say "comprehensions and generator expressions".
> Since "X comprehensions" are advertised as and intended to be 
> functionally equivalent to `X(generator expression)', I use just 
> "generator expressions" to refer to all.
> That's accurate because the common part with the distinctive syntax -- 
> which is the thing referred to when addressing them all -- effectively 
> _is_ a generator expression (the syntax differences in the leading 
> term are insignificant), what wraps it is of no concern.
> So, no new terms are necessary, but someone who cares may add a note 
> to the docs to this effect.

>> Maybe it's not too late to start calling the latter "generator 
>> comprehensions" so that maybe by the year 2025 we can say 
>> "comprehensions" and everyone will understand we mean all four types?

Oh, I see. So, "comprehension" is actually the official term for this 
"distinctive syntax", and the fact that "generator expressions" came to 
use it is but a coincidence.

In that case, we can do a Solomon's decision: mention _both_ that 
"comprehension" is the official term for the syntax in GE's reference 
entry, _and_ the fact that "X comprehensions" are effectively wrapped 
GEs in their reference entries.

Then everyone will learn both terminologies and could choose which is 
more convenient to use.

>> FWIW more people should start using "list display" etc. for things 
>> like [a, b, c].
>> -- 
>> --Guido van Rossum (python.org/~guido <http://python.org/%7Eguido>)
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