Bug Report: inferred_value doesn't propagate to the subscript of a list about pyanalyze HOT 4 CLOSED

Thanks for the report! The issue here is actually that pyanalyze doesn't deal with list.__getitem__ at all. This is basically an instance of #64, a place where it unexpectedly isn't able to infer something.

Subscripts get handled in https://github.com/quora/pyanalyze/blob/master/pyanalyze/name_check_visitor.py#L3327. It has some special cases for SequenceIncompleteValue, so you'll see int subscripts work for some cases where pyanalyze has a precise type, but for general lists it will just fall back to the return type of list.__getitem__. Because that method is overloaded in typeshed (https://github.com/python/typeshed/blob/master/stdlib/builtins.pyi#L776), pyanalyze doesn't know what to do with it and just returns Any.

This isn't exactly going to be trivial to fix. I see two ways out:

• Add support for overloads (#182). That's going to be a pretty big project. I'll probably take it on after I get protocols working, but it may be a while.
• Add an implementation function for list.__getitem__ in implementations.py, similar to the existing one for dict.__getitem__. Doing this will allow us to get rid of some more special casing in name_check_visitor.py. We'd also want a very similar impl for tuple.__getitem__.

The second option shouldn't be too hard if you're interested in taking it on. I'd recommend looking at the existing implementation functions for dict.__getitem__ and other list methods as examples.

(Also, sorry for not responding earlier; I was out of town.)

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#241 should fix this.

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Nice!

I'm glad to see there's so much recent activity. Mind if I ask what's your new goal?

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An internal use case came up that required some pyanalyze changes. While implementing that I noticed a bunch of other bugs that affected us, so I decided to fix them. The one from #242 is especially nasty; I still have a lot of things I need to fix internally before I can merge that one. I'm thinking of cutting a release once I get all these resolved.

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