UnicodeDecodeError on importing pyplot in python2

[AndreySV]

Bug report

Bug summary

UnicodeDecodeError on importing pyplot If some module in call stack is located in directory with non-ascii character in path. The problem is that traceback.format_stack() returns list of 'str' objects in python2. This problem happens only on python2.

Code for reproduction
Create two modules in a directory with a non-ascii character in the path.

#!/usr/bin/env python
# first_module.py
import second_module

# second_module.py
import matplotlib.pyplot

Run first module.

$ python2 first_module.py

Actual outcome

Following traceback happens

Traceback (most recent call last):
  File "./a.py", line 3, in <module>
    import second_module
  File "/home/developer/WorkData/PLC/beremiz/tmp/xыв/beremiz/second_module.py", line 3, in <module>
    import matplotlib.pyplot
  File "/usr/lib/python2.7/dist-packages/matplotlib/pyplot.py", line 71, in <module>
    from matplotlib.backends import pylab_setup
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/__init__.py", line 16, in <module>
    line for line in traceback.format_stack()
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/__init__.py", line 18, in <genexpr>
    if not line.startswith('  File "<frozen importlib._bootstrap'))
UnicodeDecodeError: 'ascii' codec can't decode byte 0xd1 in position 50: ordinal not in range(128)

Matplotlib version

• Operating system: Debian Buster
• Matplotlib version: 2.2.2
• Matplotlib backend (print(matplotlib.get_backend())): 'WX"
• Python version: 2.7.15

[AndreySV]

Suggested in comment change:

_backend_loading_tb = b"".join(
    line for line in traceback.format_stack()
    # Filter out line noise from importlib line.
    if not line.startswith(b'  File "<frozen importlib._bootstrap'))

seems to fix the problem. In python2 crash doesn't happen anymore and the code looks to work with python 3.6 either.

[tacaswell]

@AndreySV Can you try the fix in #11957 ? It is slightly different, but should have the same effect.

[AndreySV]

all good like originally suggested changed.

[Zac-HD]

@tacaswell looks like merging #11957 didn't automatically close this?