bin(x) 轉換二進制

bin(x)

Convert an integer number to a binary string prefixed with 「0b」. 
轉換一個整型數字爲一個前綴是「0b」的二進制字符串
If x is not a Python int object, it has to define an __index__() method that returns an integer. 
若是x不是 int 對象，必須定義一個返回整型的__index__() 方法

>>> bin(3)
'0b11'
>>> bin(-10)
'-0b1010'