This piece of code will raise an error:

    import os
    import sys

    os.set_blocking(sys.stdin.fileno(), False)
    sys.stdin.read()

Error:

>   TypeError: can't concat NoneType to bytes

Not sure if this is relevant (for a different version of Python): https://bugs.python.org/issue24560

This is the same story as in Issue 35762. Both “sys.stdin” and “subprocess.Popen.stderr” (when universal_newlines=True is enabled) use the TextIOWrapper class, which I don’t think was implemented with non-blocking mode in mind.

Issue 24560 is similar, but is about an older class “codecs.StreamReader”.

Martin, did you mean to close this as a duplicate?

I wasn’t sure about closing it, in case Cyker came back with more details. E.g. what was the use case? Were they mislead by the documentation? Do they just think the error should be different, or do they think there should be no error in this case?

But I suppose we can close this and keep discussion about non-blocking text input together in the existing reports.