Detailed introduction to Python's built-in bin function

English documentation:

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.

Instructions:

1. Convert an integer number into a binary string

>>> b = bin(3) 
>>> b
'0b11'
>>> type(b) #获取b的类型
<class &#39;str&#39;>

2. If the parameter x is not an integer, then x must define an __index__() method, and the method return value must be an integer.

2.1 If the object is not an integer, an error will be reported

>>> class A:
    pass

>>> a = A()
>>> bin(a) 
Traceback (most recent call last):
  File "<pyshell#15>", line 1, in <module>
    bin(a)
TypeError: &#39;A&#39; object cannot be interpreted as an integer

2.2 If the object defines the __index__ method, but the return value is not an integer, an error will be reported

>>> 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 The object defines _ _index__ method, and the return value is an integer, convert the __index__ method return value into a binary string

>>> class C:
    def __index__(self):
        return 3

>>> c = C()
>>> bin(c)
'0b11'

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