Python

name: Python slug: python version: 1.0.1 description: Write reliable Python avoiding mutable defaults, import traps, and common runtime surprises. metadata: {"clawdbot":{"emoji":"🐍","requires":{"bins":["python3"]},"os":["linux","darwin","win32"]}}

Quick Reference

Critical Rules

• def f(items=[]) shares list across all calls — use items=None then items = items or []
• is checks identity, == checks equality — "a" * 100 is "a" * 100 may be False
• Modifying list while iterating skips elements — iterate over copy: for x in list(items):
• GIL prevents true parallel Python threads — use multiprocessing for CPU-bound
• Bare except: catches SystemExit and KeyboardInterrupt — use except Exception:
• UnboundLocalError when assigning to outer scope variable — use nonlocal or global
• open() without context manager leaks handles — always use with open():
• Circular imports fail silently or partially — import inside function to break cycle
• 0.1 + 0.2 != 0.3 — floating point, use decimal.Decimal for money
• Generator exhausted after one iteration — can't reuse, recreate or use itertools.tee
• Class attributes with mutables shared across instances — define in __init__ instead
• __init__ is not constructor — __new__ creates instance, __init__ initializes
• Default encoding is platform-dependent — always specify encoding='utf-8'

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這是一份專注於 Python 常見陷阱的實用速查包，涵蓋型別、函式、併發、測試等多個方面，結構清晰、分類明確，適合快速查閱和避坑。優點是內容精煉、針對性強，Critical Rules 設計便於快速定位關鍵問題；不足之處在於部分主題講解較淺，缺少程式碼示例和場景化指引，整體更像是錯誤清單而非全面的實踐指南。基礎避坑夠用，但深度和系統性有提升空間。