Lambda, map, filter

Why this matters

PEP 8 and most style guides (Google, Black-adjacent) prefer comprehensions over map/filter, but lambdas remain load-bearing in pandas .apply, sorted(key=...), and functools.reduce. Knowing when to reach for operator.itemgetter over lambda is a real perf win.

Common pitfalls

• Assigning a lambda to a name — f = lambda x: x+1 fails linting; use def for anything named.
• Late binding in loop-defined lambdas — [lambda: i for i in range(3)] all return 2; pin with lambda i=i: i.
• Reaching for map(lambda x: x.name, items) when operator.attrgetter('name') is faster and clearer.