unused variables in list comprehension not reported #593

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1. asottile commented on Nov 17, 2020

   

   asottile

   on Nov 17, 2020

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   I agree this particular example should probably produce an error, but pyflakes is a bit timid about assignments in unpackings

   for example, should this produce a warning (pyflakes currently assumes any sort of unpacking can introduce variables that don't need to be referenced)?

   return [f'{x} for x, y in items]
2. lilydjwg commented on Nov 18, 2020

   

   lilydjwg

   on Nov 18, 2020

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   Aren't unused names expected to be prefixed with _? If not, maybe pyflakes can detect missing f-prefixes in another way?

   This kind of errors is not easy to notice otherwise: the types check with any issue; the {x} syntax inside normal strings is also special (for .format) so it's highlighted anyway.
3. asottile commented on Nov 26, 2020

   

   asottile

   on Nov 26, 2020

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   that's not something that's errorable either

   consider this valid snippet:

   FMT_S = 'foo {bar}'
   
   def make_thing():
       return FMT_S.format(bar=...)

   (of course this is a silly example that could be inlined, but it is still a case that comes up). this would introduce a high-false-positive rule which isn't really appropriate for pyflakes and is better left to a flake8 plugin or pylint