I think it is worth to improve the error message in the write() method of binary files.

>>> sys.stdout.write(b'')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: write() argument must be str, not bytes
>>> sys.stdout.buffer.write('')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: a bytes-like object is required, not 'str'
>>> sys.stdout.buffer.raw.write('')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: a bytes-like object is required, not 'str'

But this is large issue. Other file-like objects (GzipFile, ZipExtFile etc) should be updated too.