Python bin() function

Updated on Nov 08, 2019


The bin() function returns the binary representation of the integer as a string.

Its syntax is as follows:

bin(number) -> binary representation
Parameter Description
number Any numeric value

Here is an example:

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>>> 
>>> bin(4) # convert decimal to binary
'0b100'
>>> 
>>> 
>>> bin(0xff) # convert hexadecimal to binary, 0xff is same decimal 255
'0b11111111'
>>> 
>>> 
>>> bin(0o24) # convert octacl to binary, 0o24 is same decimal 20
'0b10100'
>>>
print(bin(4))
print(bin(0xff))
print(bin(0o24))

bin() with User-defined object #


To use bin() with user-defined objects, we have to first overload the __index__() method. The __index__() method is used to coerce an object to an integer, in the context of slicing and index. For instance, consider the following:

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>>>
>>> l = [1, 2, 3, 4, 5]
>>>
>>> x, y = 1, 3
>>>
>>>
>>> l[x]
2
>>> 
>>>
>>> l[y]
4
>>> 
>>>
>>> l[x:y]
[2, 3]
>>>
l = [1, 2, 3, 4, 5]
x, y = 1, 3
print(l[x])
print(l[y])
print(l[x:y])

When we access items in a list using indexing and slicing, internally Python calls __index__()  method of the int object.

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>>> 
>>> l[x.__index__()] # same as l[x]
2
>>> 
>>>
>>> l[y.__index__()] # same as l[y]
4
>>> 
>>> 
>>> l[x.__index__():y.__index__()] # # same as l[x:y]
[2, 3]
>>>
l = [1, 2, 3, 4, 5]
x, y = 1, 3
print(l[x.__index__()])
print(l[y.__index__()])
print(l[x.__index__():y.__index__()])

In addition to bin(), the __index__() method is also called when you call hex(), and oct()  on the object. Here is an example:

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>>>
>>> class Num:
...     def __index__(self):
...         return 4
... 
>>>
>>> l = [1, 2, 3, 4, 5]
>>>
>>> 
>>> n1 = Num()
>>>
>>> 
>>> bin(n1)
0b100
>>>
>>> 
>>> hex(n1)
0x4
>>> 
>>> 
>>> oct(n1)
0o4
>>> 
>>> 
>>> l[n1]
5
>>> 
>>> 
>>> l[n1.__index__()]
5
>>>
class Num:
    def __index__(self):
        return 4

l = [1, 2, 3, 4, 5]

n1 = Num()

print(bin(n1))
print(hex(n1))
print(oct(n1))
print(l[n1])
print(l[n1.__index__()])

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