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
當我們說「
expression
是真值（
expression
is true）」，就代表
bool(expression)
會回傳
True
。
變數和其他參考
Python 程式透過
參考
（
references
） 來存取資料值。一個
參考
是指涉
（refers to）某個值（物件）的一個「名稱（name）」。參考以變數、屬性
或項目的形式出現。在 Python 中，一個變數或其他參考沒有固有的型別。
一個參考在某個時間點所繫結（bound）的物件永遠都會有型別，但一個給
定的參考在程式執行的過程中可能會被繫結至各種型別的物件。
變數
Python 中沒有「宣告（declarations）」。一個變數的存在始於
繫結
（
binds
）該變數的一個述句（換句話說，就是設定一個名稱持有某個物件
的參考）。你也可以
解除
一個變數的
繫結
（
unbind
），重置該名稱讓它不再
持有一個參考。指定述句（assignment statements）是繫結變數與其他參考
最常見的方式。
del
述句則會解除參考的繫結。
繫結一個已經繫結過的參考也叫做它的
重新繫結
（
rebinding
）。每當我們
提到繫結時，我們也隱含地包括了重新繫結（除了我們明確排除它的地
方 ）。 重新繫結或解除繫結對於參考所繫結的物件而言沒有什麼影響，只
不過一個物件會在沒有東西參考它時消失。清理沒有參考的物件就叫做
記
憶體回收
（
garbage collection
）。
你能以任何識別字（identifier）來為一個變數命名，除了 Python ...
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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.