I stumbled across the problem reported in https://bugs.python.org/issue25030 on Python 3.8:

>>> with open('x.txt', 'a') as fp:
...   fp.seek(0, whence=os.SEEK_END)
... 
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
TypeError: seek() takes no keyword arguments

Which I coded with a keyword argument because the documentation says so:

   seek(offset, whence=SEEK_SET)

See https://docs.python.org/3.8/library/io.html#io.IOBase.seek

The fix for issue issue25030 changed the documentation to:

   seek(offset[, whence])

and supposedly was integrated into 2.7, 3.4, and the default branch back then.

It seems the fix got lost?