**Why List Semantics Matter:** lst += [x] mutates in-place; lst = lst + [x] creates new list—affects performance and shared references. In pipelines, unintended mutation causes subtle bugs.
**Operations & Complexity:** append O(1) amortized; insert(0, x) O(n); extend O(k); in O(n). For repeated prepend: use collections.deque (O(1) appendleft). For sorted insert: bisect.insort O(n).
**Production Gotcha:** Never modify a list while iterating—use [x for x in lst if cond] or iterate over lst[:]....
The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations. It covers performance optimization strategies, common pitfalls to avoid, and real-world examples from companies like McKinsey. The answer also includes follow-up discussion points that interviewers commonly explore.
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