Python中块前冒号的目的是什么? [英] What is the purpose of the colon before a block in Python?

问题描述

Python 中块前冒号的作用是什么?

What is the purpose of the colon before a block in Python?

示例:

if n == 0:
    print "The end"

推荐答案

冒号用于声明缩进块的开始.

The colon is there to declare the start of an indented block.

从技术上讲，没有必要；您可以在块完成后缩进和取消缩进.然而，基于 Python koan 显式优于隐式"(EIBTI)，我相信 Guido 故意使冒号成为强制性的，所以 任何 声明 应该 后跟缩进代码都以冒号结尾.(如果您在冒号之后继续，它也允许单行，但这种样式并未广泛使用.)

Technically, it's not necessary; you could just indent and de-indent when the block is done. However, based on the Python koan "explicit is better than implicit" (EIBTI), I believe that Guido deliberately made the colon obligatory, so any statement that should be followed by indented code ends in a colon. (It also allows one-liners if you continue after the colon, but this style is not in wide use.)

它还使语法感知自动缩进编辑器的工作更容易，这也计入决策.

It also makes the work of syntax-aware auto-indenting editors easier, which also counted in the decision.

这个问题原来是一个Python 常见问题解答，我找到了 Guido here:

This question turns out to be a Python FAQ, and I found one of its answers by Guido here:

为什么 if/while/def/class 语句需要冒号?

需要冒号主要是为了提高可读性(实验性 ABC 语言的结果之一).考虑一下:

The colon is required primarily to enhance readability (one of the results of the experimental ABC language). Consider this:

if a == b 
    print a

对比

if a == b: 
    print a

请注意第二个更容易阅读.进一步注意冒号如何引出此常见问题解答中的示例；这是英语的标准用法.

Notice how the second one is slightly easier to read. Notice further how a colon sets off the example in this FAQ answer; it’s a standard usage in English.

另一个次要原因是冒号使具有语法突出显示的编辑器更容易；他们可以查找冒号来决定何时需要增加缩进，而不必对程序文本进行更精细的解析.

Another minor reason is that the colon makes it easier for editors with syntax highlighting; they can look for colons to decide when indentation needs to be increased instead of having to do a more elaborate parsing of the program text.

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