[Python-ideas] Fwd: Fwd: Fwd: unpacking generalisations for list comprehension

[Steven D'Aprano]

On Mon, Oct 17, 2016 at 10:33:32PM +0200, Sven R. Kunze wrote:

> Sorry? You know, I am all for real-world code and I also delivered: 
> https://mail.python.org/pipermail/python-ideas/2016-October/043030.html

Your example shows the proposed:

    [*(language, text) for language, text in fulltext_tuples if language == 'english']

which can be written as:

    [x for language, text in fulltext_tuples for x in (language, text) if language == 'english']

which is only ten characters longer. To me, though, there's simply no 
nice way of writing this: the repetition of "language, text" reads 
poorly regardless of whether there is a star or no star.

If I were doing this more than once, I'd be strongly inclined to invest 
in a simple helper function to make this more readable:

    def filter_and_flatten(language, fulltext):
        for lang, text in fulltext:
            if lang == language:
                yield lang
                yield text

    filter_and_flatten('english', fulltext_tuples)


In some ways, list comprehensions are a trap: their convenience and ease 
of use for the easy cases lure us into using them when we ought to be 
using a generator. But that's just my opinion.



-- 
Steve