example:

Python 2.7.14 |Anaconda, Inc.| (default, Dec  7 2017, 17:05:42) 
[GCC 7.2.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import warnings
>>> warnings.warn(u'blé')
>>> warnings.warn('blah')
__main__:1: UserWarning: blah

the warnings.warn_explicit function seems to be the part that is failing. On a machine which doesn't use anaconda it fails in an identical manner.

if you do:
>>> with warnings.catch_warnings(record=True) as w:
...   warnings.warn(u'blé')
... 
>>> w
[<warnings.WarningMessage object at 0x7ffadb35b190>]
>>> w[0].message
UserWarning(u'bl\xe9',)


I can get that it fails with unicode (though it's annoying) but the silent fail is really bad imo.

I think this a known limitation as per https://bugs.python.org/issue23637#msg239361 where non-ASCII characters would require byte string. I couldn't find the relevant documentation for it though.

$ ./python.exe
Python 2.7.15+ (remotes/upstream/2.7:69d0bc1430, Sep 24 2018, 16:02:09)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import warnings
>>>
>>> warnings.warn(b'blé')
__main__:1: UserWarning: blé
>>> warnings.warn(u'blé')
>>>

Thanks

I looked some more into the linked issue and I think this is an explicit decision and the comment in the code indicates that the warning will be lost : https://github.com/python/cpython/blob/69d0bc1430d2e9cddf0b39054ddcb86dbbe7927e/Lib/warnings.py#L34 . I understand your perspective on failing silently but I am proposing to close this since enabling the error by removing UnicodeDecodeError in the except clause will be an incompatible change at this point.

Thanks

Since Nick had some issue on adding a message to the issue I am adding the email sent to me as a message below : 


(sorry I can't see how to post a reply message on the bugs page, I'm still new to this)

anyhow here's what I wanted to post:

Thanks for finding the bug!
Maybe a preferable behaviour would be to split the error types
 - an IOError could still pass (I'm really not sure what the ideal treatment in that case is
 - a Unicode error would still print a warning but it would be something like a generic 'warning: non-standard text found in warning text so only printing this' (I'm sure there's something better sounding / more consistent with other warnings but I don't know them that well)

so the code would look something like:
except (UnicodeError):
    message = "non-standard text found in warning text so only printing this"
    file.write(formatwarning(message, category, filename, lineno, line))
except (IOError):
        pass # the file (probably stderr) is invalid - this warning
 gets lost.



but I'm not sure if an IOError inside the UnicodeError handling would still be caught (?)

anyhow I'm not sure how standard/appropriate a generic warning would be within the broader context of python (?) I think for us we'll probably just bite the bullet and switch to python3 to avoid this kind of thing since we'll potentially have a lot of unicode messages in the near future.

thanks again,
Nick Parslow

Python 2.7 is no longer supported, so I think this issue should be closed.