Month: August 2026

Three tools from the collections module that replace loops you have written by hand many times, and the one defaultdict behaviour that surprises people.

One decorator writes __init__, __repr__ and __eq__ for you. Defaults, frozen instances, ordering, post-init and the default_factory rule.

What with guarantees, how to write __enter__ and __exit__, the contextlib shortcut, and how to swallow an exception on purpose.

One asks whether two names point at the same object, the other asks whether the values match. Plus why small numbers seem to break the rule.

Number formats, alignment, the equals sign debug trick, dates and literal braces. The formatting cheatsheet with real output.

Assignment does not copy. A shallow copy copies one level. Here is exactly where the line falls and what copy.deepcopy does about it.

The syntax, filtering, nesting, dict and set versions, and when a generator expression is the better choice.

A decorator is a function that takes a function and returns a new one. Build one from scratch, then see why functools.wraps matters.

What the star and the double star actually do, the order the parameters have to be in, and how to pass arguments straight through to another function.

A list used as a default argument is created once, not once per call. Here is what that looks like when it goes wrong, and the one line fix.