August 2015
Intermediate to advanced
384 pages
7h 42m
Chinese
Content preview from 高效能PYTHON程式設計
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第二章
在最佳化期間進行單元測試以維持正確性
如果你還沒對你的程式碼進行單元測試，那麼，你很可能正在傷害你的長期生產力。Ian
有很尷尬的經驗，他曾經花了一整天的時間最佳化他的程式碼，但因為不方便的關係而
將單元測試停掉，最後卻發現，效能大幅提升的原因竟然是因為毀損了他正在改進的一
部分演算法。你不需要犯這樣的錯誤，一次都不要。
除了單元測試之外，你也應該考慮使用
coverage.py
，它檢查哪幾行程式碼被你的測試
所涵蓋，並且識別出未被涵蓋的部分。這迅速讓你釐清是否正在測試你要最佳化的程式
碼，因此，任何可能在最佳化過程中潛伏進來的錯誤都會迅速地被捕捉。
無操作 @profile 裝飾器
如果你的程式碼使用來自
line_profiler
或
memory_profiler
的
@profile
，你的單元測試
會發生
NameError
的例外，原因是，單元測試框架不會把
@profile
裝飾器注入本地名稱
空間。這裡所顯示的無操作裝飾器（no-op decorator）會解決這個問題，將它增加到你
正在測試的程式碼區塊，並且在完成時移除它，是最容易的做法。
透過使用無操作裝飾器，你不需要修改你的程式碼，就能夠執行你的單元測試。這表
示，你能夠在每次由效能分析引導的最佳化之後執行你的測試，所以你不會因為不良的
最佳化步驟而導致意外的錯誤。
假設我們有範例 2-20 所示的簡單
ex.py
模組，它包含單元測試（針對
nosetests
）以及
我們一直在使用
line_profiler
或
memory_profiler
進行效能分析的函式。 ...
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