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map with lambda is broken in Python 2; gives '<Erased>' object is not iterable #5210
Description
@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):
a = [(1, ''), (2, '')]
b = map(lambda (i, s): str(i) + s, a)Before that PR, this would pass; now it gives
_.py:2: error: '<Erased>' object is not iterable
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): ....
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gvanrossum commentedon Jun 12, 2018
Actually I'm not sure if it occurs with ifilter() -- the one occurrence is inside an imap() call:
All the other functions involved are overloaded. Oh, I also saw an occurrence with max(), which is also overloaded.
gvanrossum commentedon Jun 12, 2018
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.
Fix leaking error messages during overload selection
Fix leaking error messages during overload selection (#5211)