colorlog doesn't strip colors when redirected to file

[borntyping]

colorlog doesn't strip colors when redirected to file

[thorstenkampe]

Further analysis: it seems like the above behaviour is the default behaviour. There is a class TTYColoredFormatter which should strip the escape sequences when the output device is not a TTY.

• On Windows color escapes are stripped regardless of whether I use ColoredFormatter or TTYColoredFormatter. This is likely because Colorlog uses colorama on Windows with the default settings ("The default behaviour is to strip if on Windows or if output is redirected (not a tty)").

• On Linux the color escapes are only stripped when redirecting stdout and using TTYColoredFormatter. This is of course a bug because logging can go to stdout and stderr but by default goes to stderr: "class logging.StreamHandler(stream=None) - [...] If stream is specified, the instance will use it for logging output; otherwise, sys.stderr will be used."

[thorstenkampe]

Minimal example to demonstrate the issue - save this as logtest.py:

import colorlog
logger  = colorlog.getLogger()
handler = colorlog.StreamHandler()
handler.setFormatter(
    colorlog.TTYColoredFormatter('%(log_color)s%(message)s%(reset)s'))
logger.addHandler(handler)
logger.error('test')

#1
./logtest.py
test             # printed red (GOOD)

#2
./logtest.py > test.txt
test             # color stripped (BAD)

#3
./logtest.py 2> test.txt
cat -v test.txt
^[[31mtest^[[0m  # color escapes NOT stripped (BAD)

[thorstenkampe]

On further investigation: when installing colorama on Linux - where it is not needed - issue #3 from above (redirecting stderr) goes away. Issue #2 (redirecting stdout) persists.

[borntyping]

This line should probably be changed so that the default stream a TTY formatter checks is stdout, matching the default stream used by the StreamHander: https://github.com/borntyping/python-colorlog/blob/master/colorlog/colorlog.py#L200