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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集合運算
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79
Python
語
言
標準程式庫模組
operator
（涵蓋於後面的「operator 模組」中）提供
attrgetter
與
itemgetter
這兩個高階函式（higher-order functions），它們
所產生的函式專門用於串列方法
sort
和內建函式
sorted
的
key=
選擇性引
數。完全相同的選擇性引數
key=
也出現在內建函式
min
和
max
中，以及標
準程式庫模組
heapq
（涵蓋於後面的「heapq 模組」中）的函式
nsmallest
和
nlargest
中。
集合運算
Python 提供各式各樣能夠套用到集合（普通的或凍結的都有）上的運算。
既然集合（sets）是容器，內建函式
len
就能接受一個集合作為其單一引
數，並回傳集合中項目的數量。集合是可迭代的（iterable），所以你可以
將它傳給接受 iterable 作為引數的任何函式或方法。在這種情況下，迭代
（iteration）的動作會以某種任意的順序產出（yield）集合中的項目。舉例
來說，對於任何的集合
S
，
min(S)
會回傳
S
中最小的項目，因為帶有單一
引數的
min
會迭代（iterate）那個引數（在此順序並不重要，因為隱含的比
較動作有遞移性）。
集合的成員資格
k in S
運算子會檢查物件
k
是否為集合
S
中的一個項目。若是，它就會回
傳
True
，否則回傳
False
。
k not in S
等同於
not (k in S)
。
集合方法
集合物件提供了數個方法，如表 3-4 中所示。非變動方法會回傳一個
結果但不會更動套用它們的物件
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