Python int to binary string?

Question

Are there any canned Python methods to convert an Integer (or Long) into a binary string in Python?

There are a myriad of dec2bin() functions out on Google... But I

Answer 1

def binary(decimal) :
    otherBase = ""
    while decimal != 0 :
        otherBase  =  str(decimal % 2) + otherBase
        decimal    //=  2
    return otherBase

print binary(10)

output:

1010

Answer 2

Unless I'm misunderstanding what you mean by binary string I think the module you are looking for is struct

Answer 3

For those of us who need to convert signed integers (range -2**(digits-1) to 2**(digits-1)-1) to 2's complement binary strings, this works:

def int2bin(integer, digits):
    if integer >= 0:
        return bin(integer)[2:].zfill(digits)
    else:
        return bin(2**digits + integer)[2:]

This produces:

>>> int2bin(10, 8)
'00001010'
>>> int2bin(-10, 8)
'11110110'
>>> int2bin(-128, 8)
'10000000'
>>> int2bin(127, 8)
'01111111'

Answer 4

one-liner with lambda:

>>> binary = lambda n: '' if n==0 else binary(n/2) + str(n%2)

test:

>>> binary(5)
'101'

EDIT:

but then :(

t1 = time()
for i in range(1000000):
     binary(i)
t2 = time()
print(t2 - t1)
# 6.57236599922

in compare to

t1 = time()
for i in range(1000000):
    '{0:b}'.format(i)
t2 = time()
print(t2 - t1)
# 0.68017411232

Answer 5

If you are willing to give up "pure" Python but gain a lot of firepower, there is Sage - example here:

sage: a = 15
sage: a.binary()
'1111'

You'll note that it returns as a string, so to use it as a number you'd want to do something like

sage: eval('0b'+b)
15

Answer 6

numpy.binary_repr(num, width=None)

Examples from the documentation link above:

>>> np.binary_repr(3)
'11'
>>> np.binary_repr(-3)
'-11'
>>> np.binary_repr(3, width=4)
'0011'

The two’s complement is returned when the input number is negative and width is specified:

>>> np.binary_repr(-3, width=3)
'101'
>>> np.binary_repr(-3, width=5)
'11101'