The originating issue occurred while using tqdm in twisted-run tests in py2 (or pytest). You end up with an io.BytesIO as the file which is unable to have a (not-encoded) unicode written to it.

import io
import sys

import tqdm

print(tqdm.__version__, sys.version, sys.platform)

x = [1, 2, 3]

f = io.BytesIO()

for y in tqdm.tqdm(x, file=f):
    pass

https://repl.it/@altendky/SnarlingRuralCustomization

('4.24.0', '2.7.15 (default, Jul 25 2018, 18:24:03) \n[GCC 6.3.0 20170516]', 'linux2')
Traceback (most recent call last):
  File "python", line 12, in <module>
TypeError: 'unicode' does not have the buffer interface

I like to document issues first, but I'll go take a look and see if I can straighten out why tqdm is trying to write unicode to an io.BytesIO that needs bytes.