Printing to STDOUT and log file while removing ANSI color codes

Question

I have the following functions for colorizing my screen messages:

def error(string):
    return '\033[31;1m' + string + '\033[0m'

def standout(string):
    return '\033[34;1m' + string + '\033[0m'

I use them as follows:

print error('There was a problem with the program')
print "This is normal " + standout("and this stands out")

I want to log the output to a file (in addition to STDOUT) WITHOUT the ANSI color codes, hopefully without having to add a second "logging" line to each print statement.

The reason is that if you simply python program.py > out then the file out will have the ANSI color codes, which look terrible if you open in a plain text editor.

Any advice?

Answer 1

The sys.stdout.isatty function might be able to help:

from sys import stdout

def error(string, is_tty=stdout.isatty()):
    return ('\033[31;1m' + string + '\033[0m') if is_tty else string

def standout(string, is_tty=stdout.isatty()):
    return ('\033[34;1m' + string + '\033[0m') if is_tty else string

That's actually one of the few uses I can think of to use a default argument that isn't set to None because default arguments are evaluated at compile time in Python rather than at runtime like in C++...

Also the behaviour can be explicitly overridden if you really need to, though that doesn't let you manipulate stdout itself when it's redirected. Is there any reason why you're not using the logging module (perhaps you didn't know about it)?

Answer 2

If you wish to print to both the terminal and to a log file, then I'd suggest using the logging module. You can even define a custom formatter, so logging to the file can purge the terminal codes:

import optparse
import logging

def error(string):
    return '\033[31;1m' + string + '\033[0m'

def standout(string):
    return '\033[34;1m' + string + '\033[0m'

def plain(string):
    return string.replace('\033[34;1m','').replace('\033[31;1m','').replace('\033[0m','')

if __name__=='__main__':
    logging.basicConfig(level=logging.DEBUG,
                        format='%(message)s',
                        filemode='w')
    logger=logging.getLogger(__name__)    
    def parse_options():    
        usage = 'usage: %prog [Options]'
        parser = optparse.OptionParser()
        parser.add_option('-l', '--logfile', dest='logfile', 
                          help='use log file')
        opt,args = parser.parse_args()
        return opt,args
    opt,args=parse_options()
    if opt.logfile:
        class MyFormatter(logging.Formatter):
            def format(self,record):
                return plain(record.msg)
        fh = logging.FileHandler(opt.logfile)
        fh.setLevel(logging.INFO)
        formatter = MyFormatter('%(message)s')
        fh.setFormatter(formatter)
        logging.getLogger('').addHandler(fh)

    logger.info(error('There was a problem with the program'))
    logger.info("This is normal " + standout("and this stands out"))

test.py prints only to the terminal.

test.py -l test.out prints to both the terminal and to the file test.out.

In all cases, the text to the terminal has color codes, while the logging has none.