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Allow any more general type for override of a method - #1524
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This is a prerequisite for fixing python#1261 because overrides with generic function type variables currently work by accident: the type variables have the same ids in the original method and the overriding method, so is_subtype on the argument type returns True. This also allows an overriding method to generalize a specific type in the original method to a type variable, as demonstrated in one of the tests (testOverrideGenericMethodInNonGenericClassGeneralize). is_subtype already determines correctly whether the override is valid, so all the hard work here is in providing a more specific error message when possible.
| if (isinstance(override, CallableType) and | ||
| isinstance(original, CallableType) and | ||
| len(override.arg_types) == len(original.arg_types) and | ||
| override.min_args == original.min_args): |
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Here it would be better to have an argument kind check instead of just min_args (the latter is from early, pre-mypy days).
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No need to do anything about the above comment now, since the same issue is also present elsewhere in the code. Maybe create an issue about not using argument counts in general, instead preferring to check argument kinds. (Or I can do it.) |
gvanrossum
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May 28, 2016
This is a prerequisite for fixing #1261 because overrides with generic function type variables currently work by accident: the type variables have the same ids in the original method and the overriding method, so is_subtype on the argument type returns True. This also allows an overriding method to generalize a specific type in the original method to a type variable, as demonstrated in one of the tests (testOverrideGenericMethodInNonGenericClassGeneralize). is_subtype already determines correctly whether the override is valid, so all the hard work here is in providing a more specific error message when possible.
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This is a prerequisite for fixing #1261 because overrides with generic
function type variables currently work by accident: the type variables
have the same ids in the original method and the overriding method, so
is_subtype on the argument type returns True.
This also allows an overriding method to generalize a specific type in
the original method to a type variable, as demonstrated in one of the
tests (testOverrideGenericMethodInNonGenericClassGeneralize).
is_subtype already determines correctly whether the override is valid,
so all the hard work here is in providing a more specific error
message when possible.