Python core III: exceptions, logging, generators, context managers

try/except/else/finally handles failure without crashing the program. Catch specific exceptions (except ZeroDivisionError), never a bare except — a bare except also swallows real bugs like typos in your own code. finally always runs, whether or not an exception happened, which is where cleanup belongs.

print() has no levels, no timestamps, and no way to turn it off in production without deleting code. The logging module gives you levels (DEBUG/INFO/WARNING/ERROR), timestamps, and configurable output — one line change routes every log call to a file or a log aggregator instead of stdout.

import logging
logger = logging.getLogger(__name__)

try:
    result = 10 / 0
except ZeroDivisionError as e:
    logger.error("division failed: %s", e)
finally:
    print("cleanup always runs")

A generator is a function with yield instead of return. Calling it doesn't run the body — it hands back an iterator that produces one value at a time, on demand. That means you can process a 10 GB log file line by line without ever holding the whole thing in memory.

def read_big_file(path):
    with open(path) as f:
        for line in f:
            yield line.strip()   # one line in memory at a time

A context manager (the with statement) guarantees cleanup runs even if the code inside raises — a file handle gets closed, a lock gets released, a connection gets returned to its pool. contextlib.contextmanager turns a generator function into one with a single decorator.