Print timestamp for logging in Python

Something like below would do:

formatter = logging.Formatter(fmt='%(asctime)s %(levelname)-8s %(message)s',
                              datefmt='%Y-%m-%d %H:%M:%S')

Have a look at the logging module for Python. You don't need to mess about with creating your own date, just let the logging module do it for you. That formatter object can be applied to a logging handler so you can just log with logger.info('This is an info message.'). No print statements required.

Here's a boilerplate procedure I use:

import logging
import sys

def setup_custom_logger(name):
    formatter = logging.Formatter(fmt='%(asctime)s %(levelname)-8s %(message)s',
                                  datefmt='%Y-%m-%d %H:%M:%S')
    handler = logging.FileHandler('log.txt', mode='w')
    handler.setFormatter(formatter)
    screen_handler = logging.StreamHandler(stream=sys.stdout)
    screen_handler.setFormatter(formatter)
    logger = logging.getLogger(name)
    logger.setLevel(logging.DEBUG)
    logger.addHandler(handler)
    logger.addHandler(screen_handler)
    return logger

>>> logger = setup_custom_logger('myapp')
>>> logger.info('This is a message!')
2015-02-04 15:07:12 INFO     This is a message!
>>> logger.error('Here is another')
2015-02-04 15:07:30 ERROR    Here is another

The datetime is calculated when the string is formed. So in your case, only once at the initialisation. Instead, you should do something like this:

def ok(hostname=None, status=None):
    output = (
        "[" + bc.OKGREEN + " OK "  + bc.ENDC + "] " +
        datetime.datetime.now().strftime("%d.%b %Y %H:%M:%S")
    )
    if hostname is not None:
        output += ' ' + hostname
    if status is not None:
        output += ' ' + status
    print output

To log, just do use ok() which will reevaluate the datetime each time.

Note that @paidhima suggestion is also good.