Python int to binary string?


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 was hoping I could use a built-in function / library.

4/30/2019 10:06:54 AM

Accepted Answer

Python's string format method can take a format spec.

>>> "{0:b}".format(37)

Format spec docs for Python 2

Format spec docs for Python 3

10/31/2017 12:19:23 PM

Python actually does have something already built in for this, the ability to do operations such as '{0:b}'.format(42), which will give you the bit pattern (in a string) for 42, or 101010.

For a more general philosophy, no language or library will give its user base everything that they desire. If you're working in an environment that doesn't provide exactly what you need, you should be collecting snippets of code as you develop to ensure you never have to write the same thing twice. Such as, for example, the pseudo-code:

define intToBinString, receiving intVal:
    if intVal is equal to zero:
        return "0"
    set strVal to ""
    while intVal is greater than zero:
        if intVal is odd:
            prefix "1" to strVal
            prefix "0" to strVal
        divide intVal by two, rounding down
    return strVal

which will construct your binary string based on the decimal value. Just keep in mind that's a generic bit of pseudo-code which may not be the most efficient way of doing it though, with the iterations you seem to be proposing, it won't make much difference. It's really just meant as a guideline on how it could be done.

The general idea is to use code from (in order of preference):

  • the language or built-in libraries.
  • third-party libraries with suitable licenses.
  • your own collection.
  • something new you need to write (and save in your own collection for later).

If you want a textual representation without the 0b-prefix, you could use this:

get_bin = lambda x: format(x, 'b')

>>> '11'

>>> '-11'

When you want a n-bit representation:

get_bin = lambda x, n: format(x, 'b').zfill(n)
>>> get_bin(12, 32)
>>> get_bin(-12, 32)

Alternatively, if you prefer having a function:

def get_bin(x, n=0):
    Get the binary representation of x.

    x : int
    n : int
        Minimum number of digits. If x needs less digits in binary, the rest
        is filled with zeros.

    return format(x, 'b').zfill(n)

As a reference:

def toBinary(n):
    return ''.join(str(1 & int(n) >> i) for i in range(64)[::-1])

This function can convert a positive integer as large as 18446744073709551615, represented as string '1111111111111111111111111111111111111111111111111111111111111111'.

It can be modified to serve a much larger integer, though it may not be as handy as "{0:b}".format() or bin().


A simple way to do that is to use string format, see this page.

>> "{0:b}".format(10)

And if you want to have a fixed length of the binary string, you can use this:

>> "{0:{fill}8b}".format(10, fill='0')

If two's complement is required, then the following line can be used:

'{0:{fill}{width}b}'.format((x + 2**n) % 2**n, fill='0', width=n)

where n is the width of the binary string.


This is for python 3 and it keeps the leading zeros !

print(format(0, '08b'))

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