PermissionError: [Errno 13] Permission denied: '/dev/stdout'

[senyai]

PermissionError: [Errno 13] Permission denied: '/dev/stdout'

[diazona]

This piqued my curiosity on Mastodon, and after investigating for a little while I have a suggestion: does it seem reasonable that render_report() should not delete a file that it didn't originally create? If so, it could try to open the file in exclusive mode, falling back to write mode, and set delete_file to True or False depending on which one worked.

Alternatively, it could try to delete the file first, before creating it, which should be safe in the sense that it's going to overwrite the file anyway. If the initial deletion fails, that's probably a good sign that it shouldn't try to delete the file afterwards either. The only way I can think of that this goes awry is if it's told to use an output file that exists and is writable but cannot be deleted, and then the report generation fails, leaving the file with potentially garbage content. But if that's a concern, it could just check whether the file is seekable() and if so, truncate it in place if deletion fails; if not, there's probably no way to undo writing that garbage content anyway.

If any of this sounds good, I'd be happy to contribute a PR (I've gotten more than enough good use out of coverage.py that it seems only fair to offer a contribution), or someone else is welcome to take these ideas and make their own PR.

[nedbat]

A simple way to reproduce:

% cat > hello.py
print("hello")
% coverage run hello.py
hello
% rm hello.py
% coverage json -q -o /dev/stdout
... (the error shown above) ...
PermissionError: [Errno 1] Operation not permitted: '/dev/stdout'