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

Greg Ewing greg.ewing at canterbury.ac.nz
Tue Oct 18 02:23:38 EDT 2016 
Steven D'Aprano wrote:

> 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.

I think the ugliness of this particular example has roots in
the fact that a tuple rather than an object with named fields
is being used, which is going to make *any* piece of code
that touches it a bit awkward.

If it were a namedtuple, for example, you could write

   [*t for t in fulltext_tuples if t.language == 'english']

or

   [x for t in fulltext_tuples if t.language == 'english' for x in t]

The latter is a bit unsatisfying, because we are having to
make up an arbitrary name 'x' to stand for an element of t.
Even though the two elements of t have quite different roles,
we can't use names that reflect those roles.

Because of that, to my eyes the version with * makes it easier
to see what is going on.

-- 
Greg
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