bin(x)
Convert an integer number to a binary string. The result is a valid Python expression. If x is not a Python int object, it has to define an __index__() method that returns an integer.
说明：
1. 将一个整形数字转换成二进制字符串
>>> b = bin(3) >>> b '0b11' >>> type(b) #获取b的类型 <class 'str'>
2. 如果参数x不是一个整数，则x必须定义一个 __index__() 方法，并且方法返回值必须是整数。
2.1 如果对象不是整数，则报错
>>> class A: pass >>> a = A() >>> bin(a) Traceback (most recent call last): File "<pyshell#15>", line 1, in <module> bin(a) TypeError: 'A' object cannot be interpreted as an integer
2.2 如果对象定义了__index__方法，但返回值不是整数，报错
>>> class B: def __index__(self): return "3" >>> b = B() >>> bin(b) Traceback (most recent call last): File "<pyshell#21>", line 1, in <module> bin(b) TypeError: __index__ returned non-int (type str)
2.3 对象定义了__index__方法，且返回值是整数，将__index__方法返回值转换成二进制字符串
>>> class C: def __index__(self): return 3 >>> c = C() >>> bin(c) '0b11'下载本文
