一切都大于无吗? [英] Is everything greater than None?

问题描述

是否有 Python 内置数据类型，除了 None，对于其中:

<预><代码>>>>不是 foo >没有任何真的

其中 foo 是那种类型的值?Python 3 怎么样?

解决方案

None 总是小于 Python 2 中的任何数据类型(参见 object.c).

在 Python 3 中，这被改变了；现在对没有合理自然排序的事物进行比较会导致 TypeError.来自 3.0新功能"更新:

<块引用>

Python 3.0 简化了排序比较的规则:

排序比较运算符(<、<=、>=、>)当操作数没有有意义的自然顺序时，引发 TypeError 异常.因此，表达式如: 1 <;'', 0 >None 或 len <= len 不再有效，例如无 引发 TypeError 而不是返回 False.一个推论是对异构列表进行排序不再有意义——所有元素必须相互比较.请注意，这不适用于 == 和 != 运算符:不同不可比较类型的对象总是相互不相等.

这让一些人感到不安，因为对包含一些 None 值的列表进行排序，并让 None 值聚集在开始或结束.有一个线程 不久前在邮件列表中提到过这个问题，但最终的一点是 Python 3 试图避免对排序做出武断的决定(这在 Python 2 中经常发生).

Is there a Python built-in datatype, besides None, for which:

>>> not foo > None
True

where foo is a value of that type? How about Python 3?

解决方案

None is always less than any datatype in Python 2 (see object.c).

In Python 3, this was changed; now doing comparisons on things without a sensible natural ordering results in a TypeError. From the 3.0 "what's new" updates:

Python 3.0 has simplified the rules for ordering comparisons:

The ordering comparison operators (<, <=, >=, >) raise a TypeError exception when the operands don’t have a meaningful natural ordering. Thus, expressions like: 1 < '', 0 > None or len <= len are no longer valid, and e.g. None < None raises TypeError instead of returning False. A corollary is that sorting a heterogeneous list no longer makes sense – all the elements must be comparable to each other. Note that this does not apply to the == and != operators: objects of different incomparable types always compare unequal to each other.

This upset some people since it was often handy to do things like sort a list that had some None values in it, and have the None values appear clustered together at the beginning or end. There was a thread on the mailing list about this a while back, but the ultimate point is that Python 3 tries to avoid making arbitrary decisions about ordering (which is what happened a lot in Python 2).

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