[Python-ideas] Temporary variables in comprehensions
mistersheik at gmail.com
Wed Feb 21 06:37:11 EST 2018
You should give an actual motivating example. I think none of these
suggestions are more readable than just writing things out as a for loop.
You argue that you want to avoid appending to a result list. In that case,
I suggest writing your pattern as a generator function.
On Thursday, February 15, 2018 at 2:03:31 AM UTC-5, fhsxfhsx wrote:
> As far as I can see, a comprehension like
> alist = [f(x) for x in range(10)]
> is better than a for-loop
> for x in range(10):
> because the previous one shows every element of the list explicitly so
> that we don't need to handle `append` mentally.
> But when it comes to something like
> [f(x) + g(f(x)) for x in range(10)]
> you find you have to sacrifice some readableness if you don't want two
> f(x) which might slow down your code.
> Someone may argue that one can write
> [y + g(y) for y in [f(x) for x in range(10)]]
> but it's not as clear as to show what `y` is in a subsequent clause, not
> to say there'll be another temporary list built in the process.
> We can even replace every comprehension with map and filter, but that
> would face the same problems.
> In a word, what I'm arguing is that we need a way to assign temporary
> variables in a comprehension.
> In my opinion, code like
> [y + g(y) for x in range(10) **some syntax for `y=f(x)` here**]
> is more natural than any solution we now have.
> And that's why I pro the new syntax, it's clear, explicit and readable,
> and is nothing beyond the functionality of the present comprehensions so
> it's not complicated.
> And I hope the discussion could focus more on whether we should allow
> assigning temporary variables in comprehensions rather than how to solve
> the specific example I mentioned above.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Python-ideas