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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序列化
|
387
值。
pickle
也會正確地序列化帶有參考循環（reference cycles）的圖。然
而，這也意味著，如果一個可變的物件
o
被多次序列化為相同的
Pickler
實體
p
，那麼
o
至
p
的第一次序列化之後對
o
所做的任何變更都不會被
儲存。
別在序列化的過程中變更物件
為了清晰度、正確性和簡單性，別在物件序列化為
Pickler
實體的過程中，更改那些被序列化的物件。
pickle
能以傳統的 ASCII 協定或幾個精簡的二進位協定之一進行序列化。
在 v2 中，ASCII 協定
0
是預設值，這是為了回溯相容性，但通常你應該明
確地請求二進位協定
2
，這個 v2 支援的協定能節省最多時間和空間。在 v3
中，協定的範圍從
0
到
4
（包含端點），預設為
3
，它通常是一個合理的選
擇，但你可以明確地指定協定
2
（以確保你所儲存的 pickles 可被 v2 程式
載入），或協定
4
，相容於早期版本，但在非常大型的物件上有效能優勢。
永遠都以協定
2
或更高的協定來進行
pickle
永遠都指定至少協定
2
。節省的空間和時間會很可觀，而
二進位格式基本上沒有缺點，除了所產生的 pickles 無法與
真的很老舊的 Python 版本相容以外。
當你重新載入物件，
pickle
會自動辨識並使用你目前的 Python 版本支援的
任何協定。
pickle
會以名稱序列化類別與函式，而非以它們的值。因此
pickle
解序列
化一個類別或函式的方式是從
pickle
序列化它的時候在其中找到那個類別
或函式的同一個模組匯入它。特別是，
pickle
通常只在類別或函式是它們 ...
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