A simple Google-style logging wrapper for Python.

This library attempts to greatly simplify logging in Python applications. Nobody wants to spend hours pouring over the PEP 282 logger documentation, and almost nobody actually needs things like loggers that can be reconfigured over the network. We just want to get on with writing our apps.

Styled somewhat after the twitter.common.log interface, which in turn was modeled after Google's internal python logger, which was never actually released to the wild, and which in turn was based on the C++ glog library.

• You and your code don't need to care about how logging works. Unless you want to, of course.
• No more complicated setup boilerplate!
• Your apps and scripts will all have a consistent log format, and the same predictable behaviours.

This library configures the root logger, so nearly everything you import that uses the standard Python logging module will play along nicely.

• Messages are always written to stderr.
• Lines are prefixed with a google-style log prefix, of the form

E0924 22:19:15.123456 19552 filename.py:87] Log message blah blah

Splitting on spaces, the fields are:

1. The first character is the log level, followed by MMDD (month, day)
2. HH:MM:SS.microseconds
3. Process ID
4. basename_of_sourcefile.py:linenumber]
5. The body of the log message.

import glog as log

log.info("It works.")
log.warn("Something not ideal")
log.error("Something went wrong")
log.fatal("AAAAAAAAAAAAAAA!")

If your app uses gflags, it will automatically gain a --verbosity flag. In order for that flag to be effective, you must call log.init() after parsing flags, like so:

import sys
import gflags
import glog as log

FLAGS = gflags.FLAGS

def main():
  log.debug('warble garble %s', FLAGS.verbosity)

if __name__ == '__main__':
    posargs = FLAGS(sys.argv)
    log.init()
    main(posargs[1:])

The C++ glog library provides a set of check macros that help document and enforce invariants. These are superior to standard python asserts because they provide a detailed message indicating the values that caused the check to fail with no additional boilerplate code. This makes code more readable. A stack trace is printed which identifies the code-path that caused the failure, making it easier to reproduce the error. Failed checks raise the FailedCheckException.

import glog as log
import math

def compute_something(a):
    log.check_eq(type(a), float) # require floating point types
    log.check_ge(a, 0) # require non-negative values
    value = math.sqrt(a)
    return value

if __name__ == '__main__':
    compute_something(10)

• check(condition)
• check_eq(obj1, obj2)
• check_ne(obj1, obj2)
• check_le(obj1, obj2)
• check_ge(obj1, obj2)
• check_lt(obj1, obj2)
• check_gt(obj1, obj2)
• check_notnone(obj1, obj2)

Happy logging!