Slice index false positive #3442

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1. gvanrossum commented on May 24, 2017

   

   gvanrossum

   on May 24, 2017

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   Probably a typeshed issue.
2. JelleZijlstra commented on May 24, 2017

   

   JelleZijlstra

   on May 24, 2017

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   I don't think so, this is mypy's general slicing check, not a specific __getitem__ override. Looks like the bug is in visit_slice_expr in checkexpr.py. The error message says that int or None is accepted, but the code only accepts int.
3. chrish42 commented on May 24, 2017

   

   chrish42

   on May 24, 2017

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   Furthermore, None as a slice index works in at least some cases:

   >>> range(10)[3:None]
   range(3, 10)
   

   So, at least for some cases, the code in visit_slice_expr should be more lenient and accept None as a slice index.
4. gvanrossum commented on May 24, 2017

   

   gvanrossum

   on May 24, 2017

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   OK, I thought mypy usually eventually defer to a dunder method, but if it doesn't in this case it's a mypy bug, perhaps related to strict optional.
5. gvanrossum

   closed this as completedin #3445on May 29, 2017
6. gvanrossum

   added a commit that references this issue on May 29, 2017

   Fix None slice bounds with strict-optional (#3445)

   ...

   This issue will close once commit 9ec8a95 is merged into the 'master' branch.

   9ec8a95