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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第 3 章 Python 語言
whentrue
與
whenfalse
這兩個子運算式中只有一個會被估算，取決於
condition
的真假值。
這個三元運算子中子運算式的順序可能有點令人困惑。推薦的風格是永遠
都在整個運算式周圍放上括弧。
數值運算
Python 提供一般的數值運算，如我們在表 3-2 中所見。數字（numbers）
是不可變的物件：當你在數字物件上進行運算，你會產生一個新的數字物
件，永遠都不會修改現有的物件。你可以透過唯讀特性
z.real
和
z.imag
來存取一個複數物件
z
的各個部分。試著重新繫結這些屬性會提出一個
例外。
一個數字的選擇性的
+
或
-
號，以及將一個浮點數字面值連接到一個虛數
以形成一個複數的
+
並非該字面值語法的一部分。它們是普通的運算子，
適用一般的運算子優先序規則（參閱表 3-2）。舉例來說，
-2**2
的估算結
果是
-4
：指數運算的優先序比單元減號（unary minus）還要高，所以整個
運算式的剖析方式是
-(2**2)
，而非
(-2)**2
。
數值轉換
你可以在任何兩個 Python 內建型別的數字之間進行算術運算（arithmetic
operations）和比較。如果運算元的型別不同，就會套用
強制轉型
（
coercion
）：Python 會將帶有「較小」型別的運算元轉為「較大」型別。
這些型別，從小到大依序是整數、浮點數、以及複數。你可以傳入一個
非複數引數給任何的內建數字型別，
int
、
float
或
complex
，來請求明確
的轉換。
int
會捨棄其引數的小數部分（如果有的話 ...
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