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gnprice opened this issue Jun 8, 2016 · 4 comments
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Mapping.{get,pop} can return default type #278

gnprice opened this issue Jun 8, 2016 · 4 comments

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@gnprice
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gnprice commented Jun 8, 2016

See #223. That PR was reverted because it caused some type errors that it shouldn't, but it's the right thing to do and we should figure out how to make it work.

@gvanrossum , what did the errors you saw (after python/mypy#1595 was fixed) look like?
@gnprice gnprice mentioned this issue Jun 8, 2016
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@rwbarton rwbarton mentioned this issue Jun 15, 2016
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@rwbarton
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See also python/mypy#738 and python/mypy#1114.

gvanrossum pushed a commit that referenced this issue Sep 15, 2016
Better signature for Mapping.get().
18b506e 
Fixes #278.

The approach here is different from what we thought before.  According
to this commit, there are three valid forms of Mapping[K, V].get():

  d.get()      # returns Optional[V]
  d.get(None)  # also returns Optional[V]  (seen in the wild)
  d.get(v)     # requires v to have type V, and returns V

So we don't allow d.get(d) where d is a type unrelated to V.  This is
a compromise, but I don't think there's much use for d.get(d) with a
default that is differently-typed than V, and when I tried it my
application code (that didn't use this) wouldn't type-check correctly.
@gvanrossum gvanrossum mentioned this issue Sep 16, 2016
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@gvanrossum gvanrossum mentioned this issue Oct 17, 2016
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@ambv ambv mentioned this issue Jan 12, 2017
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@euresti
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euresti commented Mar 20, 2017

If I understand correctly this looks fixed by #822
@gnprice: Is it what you wanted?

@JelleZijlstra
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I think it's fixed for get but not pop.

@euresti
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euresti commented Mar 20, 2017

Oh yeah. And we use the pop version a lot. That sounds like something I can help out with.

euresti pushed a commit to euresti/typeshed that referenced this issue Mar 20, 2017
Let MutableMapping.pop take a different default type.
52f3854 
This is particularly useful for the idiom `d.pop(k, None)` to remove an item if it exists.

Fixes python#278
@euresti euresti mentioned this issue Mar 20, 2017
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ambv pushed a commit that referenced this issue Mar 20, 2017
@euresti @ambv
Let MutableMapping.pop take a different default type. (#1044)
2fdcd2e 
This is particularly useful for the idiom `d.pop(k, None)` to remove an item if it exists.

Fixes #278
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4 participants
@rwbarton @gnprice @JelleZijlstra @euresti