Prevent encoding errors in Python

Question

I have scripts which print out messages by the logging system or sometimes print commands. On the Windows console I get error messages like

Traceback (most recent call last):
  File "C:\Python32\lib\logging\__init__.py", line 939, in emit
    stream.write(msg)
  File "C:\Python32\lib\encodings\cp850.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_map)[0]
UnicodeEncodeError: 'charmap' codec can't encode character '\u2019' in position 4537:character maps to <undefined>

Is there a general way to make all encodings in the logging system, print commands, etc. fail-safe (ignore errors)?

Answer 1

The problem is that your terminal/shell (cmd as your are on Windows) cannot print every Unicode character.

You can fail-safe encode your strings with the errors argument of the str.encode method. For example you can replace not supported chars with ? by setting errors='replace'.

>>> s = u'\u2019'
>>> print s
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python27\lib\encodings\cp850.py", line 12, in encode
    return codecs.charmap_encode(input,errors,encoding_map)
UnicodeEncodeError: 'charmap' codec can\'t encode character u'\u2019' in position
 0: character maps to <undefined>
>>> print s.encode('cp850', errors='replace')
?

See the documentation for other options.

Edit If you want a general solution for the logging, you can subclass StreamHandler:

class CustomStreamHandler(logging.StreamHandler):

    def emit(self, record):
        record = record.encode('cp850', errors='replace')
        logging.StreamHandler.emit(self, record)