Honor return type of __new__
#7188
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This basically follows the approach Jukka laid out in #1020 four years ago: * If the return type is Any, ignore that and keep the class type as the return type * Otherwise respect `__new__`'s return type * Produce an error if the return type is not a subtype of the class. The main motivation for me in implementing this is to support overloading `__new__` in order to select type variable arguments, which will be useful for subprocess.Popen. Fixes #1020.
ilevkivskyi
reviewed
Jul 10, 2019
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Thanks! Generally looks good, but there is one suspicious place.
How hard would be to support a similar feature for __init__? (Like in my comment on typeshed.) Essentially, people often implement such logic (type argument specification) in __init__, see an important example #4236 (default value for type variable).
mypy/checkmember.py
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| """Create a type object type based on the signature of __init__.""" | ||
| variables = [] # type: List[TypeVarDef] | ||
| variables.extend(info.defn.type_vars) | ||
| variables.extend(init_type.variables) | ||
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| is_new = True |
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This looks suspicious for two reasons:
- You unconditionally override an argument with an opposite default.
- Just below it appears in an
if
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Oh hm. That was testing code that survived because it works without it, since NoneTyp won't trigger the isinstance check...
ilevkivskyi
approved these changes
Jul 10, 2019
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This basically follows the approach Jukka laid out in #1020 four years ago:
the return type
__new__'s return typeThe main motivation for me in implementing this is to support
overloading
__new__in order to select type variable arguments,which will be useful for subprocess.Popen.
Fixes #1020.