This comes up pretty often. Every example can be replaced by a loop over a
single item list. It's a bit idiomatic, but not difficult. Many, as you
note, can use the new walrus operator instead.
[price for price in [item.get('price')] for item in basket if price is not
None]
On Mon, Jul 15, 2019 at 10:21 AM Fabrizio Messina <[email protected]>
wrote:
> Hello,
>
> It is likely not the first time such a proposal is being made but let's
> see.
> I would like to explicitly set variable names in list comprehensions using
> a where keyword, eventually set after the if keyword:
>
> [price for item in basket if price is not None where price := item.get(
> 'price')]
>
> For this example one could use the walrus operator which is indeed
> smaller:
> [price for item in basket if price := item.get('price') is not None]
>
> But I fell that this approach is a bit opportunistic as one is doing two
> things at a time, if you allow me more lines for a somewhat more complex
> example:
>
> [
> price * (1 + vat)
> for
> item in basket
> if
> price is not None
> where
> price := item.get('price')
> vat := get_vat(item, user)
> ]
>
> Now this example may look pretty stupid and probably one may simply use
> for loop, but I feel that this kind of Haskell-like where inside of list
> comprehension will let the programmer have a space where they can
> explicitly state the variables.
>
> Best regards,
> Fabrizio
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