Python:假与 0 [英] Python: False vs 0

问题描述

在 PHP 中，您使用 === 表示法来测试 TRUE 或 FALSE 与 1 或<代码>0.

In PHP you use the === notation to test for TRUE or FALSE distinct from 1 or 0.

例如 if FALSE == 0 返回 TRUE，if FALSE === 0 返回 FALSE.因此，在以 0 为基数进行字符串搜索时，如果相关子字符串的位置正好在开头，您会得到 0，PHP 可以将其与 FALSE 区分开来.

For example if FALSE == 0 returns TRUE, if FALSE === 0 returns FALSE. So when doing string searches in base 0 if the position of the substring in question is right at the beginning you get 0 which PHP can distinguish from FALSE.

有没有办法在 Python 中做到这一点?

Is there a means of doing this in Python?

推荐答案

在 Python 中，

In Python,

• is 运算符测试身份(False is False，0 is not False).

• The is operator tests for identity (False is False, 0 is not False).

== 运算符，用于测试逻辑相等(因此 0 == False).

The == operator which tests for logical equality (and thus 0 == False).

从技术上讲，这些都不完全等同于 PHP 的 ===，后者比较逻辑相等和类型 - 在 Python 中，a == b 和 type(a) 是类型(b).

Technically neither of these is exactly equivalent to PHP's ===, which compares logical equality and type - in Python, that'd be a == b and type(a) is type(b).

is 和 == 之间的一些其他区别:

Some other differences between is and ==:

• {} == {}，但 {} 不是 {}(列表和其他可变类型也是如此)
• 但是，如果 a = {}，则 a 是一个(因为在这种情况下它是对同一个实例的引用)

• {} == {}, but {} is not {} (and the same holds true for lists and other mutable types)
• However, if a = {}, then a is a (because in this case it's a reference to the same instance)

• "a"*255 不是 "a"*255"，但在大多数实现中，"a"*20 是 "a"*20，因为如何Python 处理字符串实习.但是，这种行为并不能保证，在这种情况下您可能不应该使用 is."a"*255 == "a"*255 并且几乎总是适合使用的比较.

• "a"*255 is not "a"*255", but "a"*20 is "a"*20 in most implementations, due to how Python handles string interning. This behavior isn't guaranteed, though, and you probably shouldn't be using is in this case. "a"*255 == "a"*255 and is almost always the right comparison to use.

• 12345 is 12345 但在大多数实现中 12345 不是 12345 + 1 - 1，类似地.您几乎总是希望在这些情况下使用相等.

• 12345 is 12345 but 12345 is not 12345 + 1 - 1 in most implementations, similarly. You pretty much always want to use equality for these cases.

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