Print raising warnings in Python rather than C++ if other error occurs (#41116)
Summary:
When we return to Python from C++ in PyTorch and have warnings and and error, we have the problem of what to do when the warnings throw because we can only throw one error.
Previously, if we had an error, we punted all warnings to the C++ warning handler which would write them to stderr (i.e. system fid 2) or pass them on to glog.
This has drawbacks if an error happened:
- Warnings are not handled through Python even if they don't raise,
- warnings are always printed with no way to suppress this,
- the printing bypasses sys.stderr, so Python modules wanting to
modify this don't work (with the prominent example being Jupyter).
This patch does the following instead:
- Set the warning using standard Python extension mechanisms,
- if Python decides that this warning is an error and we have a
PyTorch error, we print the warning through Python and clear
the error state (from the warning).
This resolves the three drawbacks discussed above, in particular it fixes https://github.com/pytorch/pytorch/issues/37240 .
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41116
Differential Revision: D22456393
Pulled By: albanD
fbshipit-source-id: c3376735723b092efe67319321a8a993402985c7
