On Linux
>>> help(open('/dev/zero').writelines)
gives
<built-in method writelines of _io.TextIOWrapper object at 0x7fed03d4e558>

However
https://docs.python.org/3/library/io.html#io.IOBase.writelines
gives

Write a list of lines to the stream. Line separators are not added, so it is usual for each of the lines provided to have a line separator at the end.

See also request that writelines support a line separator.
https://mail.python.org/archives/list/python-ideas@python.org/thread/A5FT7SVZBYAJJTIWQFTFUGNSKMVQNPVF/#A5FT7SVZBYAJJTIWQFTFUGNSKMVQNPVF

It does for me:

>>> help(open("nul").writelines)
Help on built-in function writelines:

writelines(lines, /) method of _io.TextIOWrapper instance
    Write a list of lines to stream.

    Line separators are not added, so it is usual for each of the
    lines provided to have a line separator at the end.

This is Windows, Python 3.9. What version did you get the problem with? If it's older, I'd say the problem has likely since been fixed.

I also can't reproduce this with a fresh build of 3b5b99da4b on Linux.

I used my default Python, which is Python 3.6. However, with 3.7 and 3.8 I get the same as Paul.

So I'm closing this as 'not a bug' (as there's not an already-fixed option for closing).

Even with 3.6 I get a different result:

```
Python 3.6.13 (tags/v3.6.13:aa73e1722e, Mar 23 2021, 15:45:49) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> help(open('/dev/zero').writelines)
Help on built-in function writelines:

writelines(lines, /) method of _io.TextIOWrapper instance

```

This appears to be because TextIOWrapper.writelines just didn't have a docstring in 3.6.  I can't explain why `help` just gave you the repr of the method, though.