python使用isinstance比较boolean和int [英] python comparing boolean and int using isinstance

问题描述

有人可以解释为什么 isinstance（）在下列情况下返回True？在编写代码时我期望False。

Can someone give me an explanation why isinstance() returns True in the following case? I expected False, when writing the code.

print isinstance(True, (float, int))
True

我的猜测是它的python的内部子类，零和一个浮点数或者int - 都评估当用作布尔值时，但不知道确切的原因。

My guess would be that its python's internal subclassing, as zero and one - wheter float or int - both evaluate when used as boolean, but don't know the exact reason.

解决这种情况的最pythonic方法是什么？我可以使用 type（），但在大多数情况下，这被认为是pythonic。

What would be the most pythonic way to solve a such a situation? I could use type() but in most cases this is considered less pythonic.

推荐答案

由于历史原因， bool 是 int 的子类，所以 True 是 int 的实例。 （最初，Python没有bool类型，返回真值的东西返回1或0. 当他们添加 bool 时，为了向后兼容，True和False必须尽可能为1和0的替换，因此是子类化。）

For historic reasons, bool is a subclass of int, so True is an instance of int. (Originally, Python had no bool type, and things that returned truth values returned 1 or 0. When they added bool, True and False had to be drop-in replacements for 1 and 0 as much as possible for backward compatibility, hence the subclassing.)

解决这个问题的正确方法取决于你认为的问题。

The correct way to "solve" this depends on exactly what you consider the problem to be.

• 如果你想 True 停止成为 int ，那么太糟糕了。这不会发生。



• 如果您想检测布尔值并以不同于其他整数的方式处理它们，您可以这样做：

• If you want True to stop being an int, well, too bad. That's not going to happen.

• If you want to detect booleans and handle them differently from other ints, you can do that:

if isinstance(whatever, bool):
    # special handling
elif isinstance(whatever, (float, int)):
    # other handling

如果要检测特定类正好的对象float 或 int ，拒绝子类，你可以这样做：

If you want to detect objects whose specific class is exactly float or int, rejecting subclasses, you can do that:

if type(whatever) in (float, int):
    # Do stuff.

如果你想检测所有的浮点数和整数，你已经这样做了。

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