Logging & Debugging

The logging module

logging adds levels, timestamps and destinations, and can be turned up or down without editing code.

import logging

logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s")
log = logging.getLogger(__name__)

log.info("Starting job")
log.warning("Disk at %d%%", 91)
try:
    1 / 0
except ZeroDivisionError:
    log.exception("Calculation failed")

breakpoint() and pdb

breakpoint() drops you into the debugger at that line. Use n (next), s (step), c (continue) and p expr (print).

def total(prices):
    result = 0
    for p in prices:
        breakpoint()   # inspect p and result here
        result += p
    return result

Use levels deliberately: DEBUG for detail, INFO for milestones, WARNING for odd events, ERROR for failures. Never log passwords or tokens.