January 2018
Intermediate to advanced
856 pages
17h 17m
Chinese
Content preview from Python 技術手冊 第三版
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collections 模組
|
249
deepcopy deepcopy(x,[memo])
製作
x
的一份深層拷貝並回傳它。深層複製意味著在參考構成的一個
有向（不一定是無循環的）圖（directed graph）中遞迴遊走（https://
en.wikipedia.org/wiki/Glossary_of_graph_theory#Walks）。為了產生形狀完全
相同的圖，有一點需要特別注意：在遊走過程中，如果碰到了對相同物件
的參考超過一次，那就不能製作出各別的拷貝。取而代之，必須使用對相
同物件的那些參考。請考慮下列簡單的例子：
sublist = [1,2]
original = [sublist, sublist]
thecopy = copy.deepcopy(original)
original[0] is original[1]
是
True
（也就是說，
original
的兩個項目指
涉相同的物件）。這是
original
重要的一個特性，而任何宣稱是它的「拷
貝」的東西，都必須保留這種特性。
copy.deepcopy
的語意確保
thecopy[0]
is thecopy[1]
也是
True
：
original
和
thecopy
的參考圖（graphs of
references）因此會有相同的形狀。避免重複的拷貝有一個重要的有益的
副作用：它防止了參考圖有循環（cycles）時會發生的無限迴圈。
copy.deepcopy
接受第二個選擇性的引數
memo
，它是一個
dict
，會將已
經被複製的物件之
id ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.