I’m using pylint as one of my linters and it explicitly warned to do it as:
logging.debug("This is a %s", a)
instead of
logging.debug("This is a %s" % a)
logging-not-lazy (W1201):
Specify string format arguments as logging function parameters Used when a logging statement has a call form of “logging.(format_string % (format_args…))”. Such calls should leave string interpolation to the logging method itself and be written “logging.(format_string, format_args…)” so that the program may avoid incurring the cost of the interpolation in those cases in which no message will be logged. For more, see PEP 282 – A Logging System | peps.python.org.