python函数每日一讲 - bool([x])

2013-01-22 10:18:19
bool([x])英文说明:Convert a value to a Boolean, using the standard truth testing procedure If x is false or omi

bool([x])

英文说明:Convert a value to a Boolean, using the standard truth testing procedure. If x is false or omitted, this returns False; otherwise it returns True. bool is also a class, which is a subclass of int. Class bool cannot be subclassed further. Its only instances are False and True.

New in version 2.2.1.

Changed in version 2.3: If no argument is given, this function returns False.

 

中文说明:将x转换为Boolean类型,如果x缺省,返回False,bool也为int的子类;

参数x:任意对象或缺省;大家注意到:这里使用了[x],说明x参数是可有可无的,如果不给任何参数则会返回False。

 

版本:在python 2.2.1中引入的新函数,在python2.3以后如果不传参数则返回False。

注意:该函数在python3中也可正常使用

实例

>>> bool(0)
False
>>> bool("abc")
True
>>> bool("")
False
>>> bool([])
False
>>> bool()
False
>>> issubclass(bool, int) #bool是一个subclass int
True

 

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