You signed in with another tab or window. Reload to refresh your session.You signed out in another tab or window. Reload to refresh your session.You switched accounts on another tab or window. Reload to refresh your session.Dismiss alert
A function, similar to cast(), which narrows a type from a union by including or excluding types.
Pitch
Often I encounter code where I know the type better than mypy. For example, a function that may return None or Any in some circumstances:
m = re.search("foo (.*)", some_string)
result = m.group(0)
This results in errors about Any, which then requires me to do cast(str, m.group(0)). But, if I make a mistake (str instead of bytes) or the types change in future, then I will miss a type error, as cast() completely overrules the type.
If instead, we could say "this is not X", then this would be a lot safer. e.g. Something like exclude(Any, m.group(0)) would ensure that any changes to the types are still reflected in the resulting type, and can also produce an error if the excluded type is no longer in the union type, thus ensuring that the code always stays relevant.
Alternatively, it could work as an include, saying what the type is, but also requiring the original type to be a superset of this. The cast() function could even be reused for this, with something like cast(str, m.group(0), narrow=True).
The text was updated successfully, but these errors were encountered:
Feature
A function, similar to
cast(), which narrows a type from a union by including or excluding types.Pitch
Often I encounter code where I know the type better than mypy. For example, a function that may return
NoneorAnyin some circumstances:This results in errors about
Any, which then requires me to docast(str, m.group(0)). But, if I make a mistake (strinstead ofbytes) or the types change in future, then I will miss a type error, ascast()completely overrules the type.If instead, we could say "this is not X", then this would be a lot safer. e.g. Something like
exclude(Any, m.group(0))would ensure that any changes to the types are still reflected in the resulting type, and can also produce an error if the excluded type is no longer in the union type, thus ensuring that the code always stays relevant.Alternatively, it could work as an include, saying what the type is, but also requiring the original type to be a superset of this. The
cast()function could even be reused for this, with something likecast(str, m.group(0), narrow=True).The text was updated successfully, but these errors were encountered: