Idiomatic Python logging: format string + args list vs. inline string formatting - which is preferred?

Question

Is it advantageous to call logging functions with format string + args list vs. formatting inline?

I\'ve seen (and written) logging code that uses inline string form

Answer 1

Avoiding inline string formatting does save some time if the current logging level filters the log message (as I expected) -- but not much:

In [1]: import logging

In [2]: logger = logging.getLogger('foo')

In [3]: logger.setLevel(logging.ERROR)

In [4]: %timeit -n 1000000 logger.warn('%s %s %s' % ('a', 'b', 'c'))
1000000 loops, best of 3: 1.09 us per loop

In [12]: %timeit -n 1000000 logger.warn('%s %s %s', 'a', 'b', 'c')
1000000 loops, best of 3: 946 ns per loop

So, as user1202136 pointed out, the overall performance difference depends on how long it takes to format the string (which could be significant depending on the cost of calling __str__ on arguments being passed to the logging function.)