在python真相测试中，bool()与==之间有什么区别吗? [英] Is there any difference between bool() vs == in python truth testing?

问题描述

我有两个问题.

1. 由bool()方法调用时，python中的任何内容(对象，类型，操作，函数..)都可以返回布尔值吗?

1. Can ANYTHING (objects, types, operations, functions..) in python return a boolean value when it is called upon by the bool() method?

下面的两行代码为什么不返回相同的答案?

Why dont the following two lines of code return the same answer?

print (float == True)  #prints False
print bool(float)      #prints True

推荐答案

==和bool()这两个是不同的. ==用于相等性测试，而bool()返回作为参数传递给它的对象的真值测试结果.

The two, == and bool(), are different. == is for equality testing, whereas bool() returns the result of truth value testing for the object passed to it as parameter.

根据bool()-

类bool([x])

返回一个布尔值，即True或False之一. x是使用标准真值测试过程转换的.如果x为false或省略，则返回False；否则为false.否则返回True.

Return a Boolean value, i.e. one of True or False. x is converted using the standard truth testing procedure. If x is false or omitted, this returns False; otherwise it returns True.

标准真相测试过程可以在文档中找到-

The standard truth testing procedure can be found in the documentation -

可以测试任何对象的真值，以便在if或while条件中使用或用作以下布尔运算的操作数.以下值被认为是错误的:

Any object can be tested for truth value, for use in an if or while condition or as operand of the Boolean operations below. The following values are considered false:

1. None

False

任何数字类型的零，例如0，0L，0.0，0j.

zero of any numeric type, for example, 0, 0L, 0.0, 0j.

任何空序列，例如''，()，[].

any empty sequence, for example, '', (), [].

任何空映射，例如{}.

实例，如果该类定义了__nonzero__()或__len__()方法，则当该方法返回整数零或布尔值False时.

instances of user-defined classes, if the class defines a __nonzero__() or __len__() method, when that method returns the integer zero or bool value False.

所有其他值都视为True-因此许多类型的对象始终为true.

All other values are considered True — so objects of many types are always true.

当您执行bool(float)时，您正在检查float的真值，即True.

When you do bool(float), you are checking the truth value for float, which is True.

但是，当您执行float == True时，您正在做相等操作(请注意，这不是真值测试，而是相等).在这种情况下，float和True不相等，从而导致False.

But when you do float == True, you are doing equality (please note this is not truth value testing, it is equality). In this case float and True are not equal so that results in False.

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