end-of-file-fixer hook does not handle permission errors well

I saw this traceback from during execution of pre-commit today:

Traceback (most recent call last):
  File "/home/someuser/.cache/pre-commit/repolz82qqa4/py_env-python3/bin/end-of-file-fixer", line 11, in <module>
    sys.exit(end_of_file_fixer())
  File "/home/someuser/.cache/pre-commit/repolz82qqa4/py_env-python3/lib/python3.5/site-packages/pre_commit_hooks/end_of_file_fixer.py", line 58, in end_of_file_fixer
    with open(filename, 'rb+') as file_obj:
PermissionError: [Errno 13] Permission denied: 'some_django_project/migrations/0023_auto_20181120_1541.py'

That file was created from inside a container… Would be nice to not have the backtrace, just an error.

Thanks!

[asottile]

You’re free to disagree 😃 – and in most cases I agree with you that a tool should produce error messages instead of stracktraces but in this case and in this particular class of tools and exceptions I don’t:

• first, the target audience of this tool is programmers
• when catching an exception, produce an actionable result: that is, take the exception you’re handed and produce a readable error message helping the user understand what to do
• In this case, there are a fractal of IO errors that are possible (not to mention MemoryError and any other flavor of “impending doom”)
• Almost all of these the tool can’t make a reasonable decision on a useful error message to display. You might say “oh just print the exception and not the frames” but in many cases you’ve removed the most useful information! The number of times I’ve seen IOError [Errno 13] Permission denied and no other information…
• except Exception as e: print(e) sucks! It’s much more likely to cause confusion (or hide bugs!) than be productive.
• The logic to implement all of the above, plus some sort of --debug option, plus the tests to ensure it would work would dwarf the contents of the actual tool!
• Developing the tool would be harder as mistake-exceptional cases may be swallowed as noops

[hartwork]

Well, if you consider showing backtraces cool and I don’t we have hit the bottom here. Let’s close this as wont-fix then?