Ten common mistakes are using mutable default arguments, confusing is with ==, shadowing built-ins, ignoring exceptions, relying on implicit global state, changing a list while iterating, using broad imports, forgetting resource cleanup, hard-coding secrets, and skipping tests.
Use None for optional mutable values:Copy
def add_item(item, items=None):
if items is None:
items = []
items.append(item)
return itemsUse == for value comparison and is for identity. Catch specific exceptions and preserve useful context. Use with for files and connections so cleanup happens even when an error occurs. Keep secrets in environment variables or a secret manager.
Readable code reduces mistakes. Prefer small functions, clear names, type hints at important boundaries, and tests for edge cases. Run a formatter and linter in CI. Review warnings instead of silencing them automatically.
The goal is not to write code that never fails. It is to make failures understandable, contained, and easy to correct.