make io classes inherit from typing IO classes #4145
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This makes these classes usable if type annotations are given as "IO" or "TextIO". In the future, we'll then be able to move open() to return a concrete class instead (python#3951).
Fixes python#3951. We use the values of the "mode" and "buffering" arguments to figure out the concrete type open() will return at runtime. (Compare the CPython code in https://github.com/python/cpython/blob/master/Modules/_io/_iomodule.c#L231.) I tested by writing a script that generated every mode/buffering combination, then running mypy with the open plugin disabled and comparing the results. This PR depends on python#4145.
Fixes python#3951. We use the values of the "mode" and "buffering" arguments to figure out the concrete type open() will return at runtime. (Compare the CPython code in https://github.com/python/cpython/blob/master/Modules/_io/_iomodule.c#L231.) I tested by writing a script that generated every mode/buffering combination, then running mypy with the open plugin disabled and comparing the results. This PR depends on python#4145.
| # Technically this is whatever is passed in as file, either a str, a bytes, or an int. | ||
| name: Union[int, str] # type: ignore |
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Why not type it as Union[str, bytes, int] then?
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I didn't want to broaden the type because nobody has complained about it, it's not directly related to the goal of this PR, and there's some chance broadening the type could cause new errors for people using the attribute.
Technically the right solution is to make various IO classes (not just this one but also at least TextIOWrapper) generic over (str, bytes, int) and give .name that generic type. But making these classes generic has the cost that now all users with --disallow-any-generics on have to specify the type parameter. That doesn't seem worth it for a rarely used attribute that nobody has even opened an issue about.
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This (3058bec) causes an error with the following now: import io
class MyStringIO(io.StringIO):
def readline(self, size=None) -> str:
return super().readline(size)
(with mypy master (0.790+dev.3adb2e952cf)) |
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That's strange, because I tried adding |
This makes these classes usable if type annotations are given as "IO" or "TextIO". In the future, we'll then be able to move open() to return a concrete class instead (python#3951).
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@JelleZijlstra given that this has been released with mypy 0.790 now, should there be an issue filed for it? (assuming it is yet not clear what the problem is / it cannot be fixed simply) |
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Yes, sounds good. |
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ok, filed python/mypy#9643. |
This makes these classes usable if type annotations are given as "IO"
or "TextIO". In the future, we'll then be able to move open() to
return a concrete class instead (#3951).
Also removed a number of redundant methods.