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Args to __new__ not recognized #982
Description
I have this code:
class C(object):
def __new__(cls, foo=None):
obj = object.__new__(cls)
obj.foo = foo
return obj
x = C(foo=12)
print(x.foo)
y = C(12)
This elicits an error complaining about the foo keyword to C, another about the foo attribute, and then one about the positional argument:
mypy_new.py:7: error: Unexpected keyword argument "foo" for "C"
mypy_new.py:8: error: "C" has no attribute "foo"
mypy_new.py:9: error: Too many arguments for "C"
This may be related to #794 -- feel free to close as a dupe if fixing that would automatically fix this. (There seem to be two separate issues here -- it doesn't turn the __new__ signature into the class signature, and it doesn't believe attributes set by __new__ become attributes of the object.)
Activity
JukkaL commentedon Nov 22, 2015
#794 is a third issue -- classes should be able to override
__new__with a different signature.Attribute assignment can be worked around by defining attributes in the class body. Inferring attributes in
__new__is hard to do in general, but we can probably support at least the most common idioms.JukkaL commentedon Nov 22, 2015
Marking as priority as this is a fundamental language feature that mypy doesn't support yet.
JukkaL commentedon Nov 22, 2015
#794 actually covers an additional issue -- using
super()with__new__.Merge branch 'call-type-with-__new__'
JukkaL commentedon Nov 29, 2015
Inferring signature from
__new__now works in the most common cases. I'm going to create separate issues for remaining limitations:__new____new__JukkaL commentedon Nov 29, 2015
Closing this as the immediate issue is resolved, but see also the follow-up issues linked to above and #794 -- they are needed for more complete
__new__support.