"BinaryIO" has no attribute "readinto"

[blazewicz]

I'm using readinto on a binary file in my project with static typing and I have a problem with typing.BinaryIO class.

Sample code reproducing error:

# foo.py
buf = bytearray(16)
with open('/dev/random', 'rb') as h:
    h.readinto(buf)
print(buf)

Script executes fine, but mypy complains about missing method "readinto".

$ python3 -V
Python 3.6.5
$ python3 -m mypy -V
mypy 0.600
$ python3 foo.py
bytearray(b'\x96\x91m\xe0\x8c\xcb\xa4h\xea\xe3.\x0c\xba\x04L7')
$ python3 -m mypy foo.py
foo.py:3: error: "BinaryIO" has no attribute "readinto"

The docs read as following:

Even though IOBase does not declare read(), readinto(), or write() because their signatures will vary, implementations and clients should consider those methods part of the interface. Also, implementations may raise a ValueError (or UnsupportedOperation) when operations they do not support are called.
source

I've checked and this is already marked as a TODO typing.pyi, so I'm just bumping the issue.

typeshed/stdlib/3/typing.pyi

Line 432 in 97d9f2e

# TODO readinto

[gvanrossum]

Agreed, readinto() should be added to BytesIO in typing.py and to both typing.pyi in typeshed.

[anderseknert]

Had the same error with getvalue() - at least I found this issue eventually. Just chipping in here to hopefully save others some time should they encounter it too.

[srittau]

This needs to be added to typing before it can be added to typeshed. Opened python/typing#659.

[JukkaL]

There may be some confusion between BytesIO and BinaryIO above. Should readinto() added to BinaryIO or BytesIO?

@anderseknert getvalue() is defined in BytesIO but not in BinaryIO, which I believe to be correct.

[anderseknert]

Oh, right, thanks for the correction @JukkaL - fortunately I found this issue due to @gvanrossum mentioning BytesIO above. The getvalue() method seems missing from BytesIO still, but perhaps that should be a separate issue.

[socketpair]

error: "IO[bytes]" has no attribute "readinto"

The same

[srittau]

Closing this here. This needs to be sorted out in typing first.