为什么是'==真不假'在Python语法错误？ [英] Why is 'True == not False' a syntax error in Python?

问题描述

与 == 工作在Python比较布尔值。但是，当我申请布尔不是运营商，结果是一个语法错误：

Comparing boolean values with == works in Python. But when I apply the boolean not operator, the result is a syntax error:

Python 2.7 (r27:82500, Sep 16 2010, 18:02:00) 
[GCC 4.5.1 20100907 (Red Hat 4.5.1-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> True == True
True
>>> False == False
True
>>> True is not False
True
>>> True == not False
  File "<stdin>", line 1
    True == not False
              ^
SyntaxError: invalid syntax
>>> 

为什么这是一个语法错误？我希望不存在虚假是一个前pression返回一个布尔值，真==＆LT; X＆GT; 是有效的语法，无论＆LT; X方式＆gt; 是一个前pression与有效的语法

Why is this a syntax error? I would expect not False to be an expression that returns a boolean value, and True == <x> to be valid syntax wherever <x> is an expression with valid syntax.

推荐答案

它拥有的在Python 运营商precedence（跨preTER认为你比较真实不，因为 == 具有更高的precedence比不是）。你需要一些括号澄清操作顺序：

It has to do with operator precedence in Python (the interpreter thinks you're comparing True to not, since == has a higher precedence than not). You need some parentheses to clarify the order of operations:

True == (not False)

在一般情况下，你不能使用不是上没有括号比较的右侧。但是，我不能想到一个情况，即你在任何时候需要使用不是上一个比较的右侧。

In general, you can't use not on the right side of a comparison without parentheses. However, I can't think of a situation in which you'd ever need to use a not on the right side of a comparison.

这篇关于为什么是'==真不假'在Python语法错误？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！