map with lambda is broken in Python 2; gives '<Erased>' object is not iterable #5210
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Actually I'm not sure if it occurs with ifilter() -- the one occurrence is inside an imap() call: owners = imap(lambda (k, v): 'owner=' + k,
ifilter(lambda (k, v): v > SET_SIZE_LOW_CUTOFF, count_by_owner.iteritems()))All the other functions involved are overloaded. Oh, I also saw an occurrence with max(), which is also overloaded. |
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There's also one occurence of on a map(None, ...) call -- not a lambda in sight. Also, it's not due to the typeshed changes -- I didn't bother changing typeshed when bisecting. |
Michael0x2a
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Fixes python#5210 (?) When mypy tries selecting an appropriate overload alternative, it swaps out the current 'msg' object with a placeholder. If this placeholder does not accumulate any error messages, we know that alternative is a successful match. Previously, we replaced only checkexpr.ExpressionChecker's msg object with the placeholder. However, since checkexpr can sometimes call checker.TypeChecker, we need to replace its msg object as well to prevent error messages that would normally be silenced from leaking. More broadly, the current overload implementation broke the invariant that both msg fields refer to the same underlying MessageBuilder object. This pull request fixes that oversight.
Michael0x2a
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Fixes #5210 When mypy tries selecting an appropriate overload alternative, it swaps out the current 'msg' object with a placeholder. If this placeholder does not accumulate any error messages, we know that alternative is a successful match. Previously, we replaced only checkexpr.ExpressionChecker's msg object with the placeholder. However, since checkexpr can sometimes call checker.TypeChecker, we need to replace its msg object as well to prevent error messages that would normally be silenced from leaking. More broadly, the current overload implementation broke the invariant that both msg fields refer to the same underlying MessageBuilder object. This pull request fixes that oversight.
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@Michael0x2a
This is a regression caused by your PR: f61c2ba Overhaul overload semantics, remove erasure, add union math (#5084).
Example (only works with Python 2 -- it's a syntax error with Python 3):
Before that PR, this would pass; now it gives
Simplifying this further by using a list of ints and a lambda with a non-unpacking argument makes the error going away.
Sorry for being so aggressive with priority etc., this prevents us from using master on our internal code base -- we get a dozen or so of errors due to this. It's not limited to map() -- I see it too for reduce(), imap(), and ifilter(), always with
lambda (x, y): ....The text was updated successfully, but these errors were encountered: