Convert decimal to binary in python

Question

Is there any module or function in python I can use to convert a decimal number to its binary equivalent? I am able to convert binary to decimal using int('[binary_value]',2), so any way to do the reverse without writing the code to do it myself?

Solution 1

all numbers are stored in binary. if you want a textual representation of a given number in binary, use bin(i)

>>> bin(10)
'0b1010'
>>> 0b1010
10

Solution 2

"{0:#b}".format(my_int)

Solution 3

Without the 0b in front:

"{0:b}".format(int_value)

Starting with Python 3.6 you can also use formatted string literal or f-string, --- PEP:

f"{int_value:b}"

Solution 4

def dec_to_bin(x):
    return int(bin(x)[2:])

It's that easy.

Solution 5

You can also use a function from the numpy module

from numpy import binary_repr

which can also handle leading zeros:

Definition:     binary_repr(num, width=None)
Docstring:
    Return the binary representation of the input number as a string.

    This is equivalent to using base_repr with base 2, but about 25x
    faster.

    For negative numbers, if width is not given, a - sign is added to the
    front. If width is given, the two's complement of the number is
    returned, with respect to that width.

View more solutions

Comments

[Sanjay Manohar]

Unlike the linked question "convert to binary string", I think this question is different. I came here looking to convert an integer to a corresponding binary array (or boolean array), and I think that would be a sensible answer.

[CopyPasteIt]

@SanjayManohar The pure string processing algorithm found here could be adapted to do what you want.

[aaronasterling]

int(bin(10), 2) yields 10. int(decToBin(10)) yields 101 and int(decToBin(10), 2) yields 5. Also, your function hit's recursion limits with from __future__ import division or python 3

[Alex Martelli]

@aaron, the latter point can be solved by switching to // (truncating division); the former, by switching the order of the two strings being summed in the return. Not that recursion makes any sense here anyway (bin(n)[2:] -- or a while loop if you're stuck on some old version of Python -- will be much better!).

[Eric]

-1 - don't return an int. Also, dec_to_bin(-1) gives ValueError: invalid literal for int() with base 10: 'b1'

[Waldo Bronchart]

Here's the format for printing with leading zero's: "{0:08b}".format(my_int)

[Patrick Ferreira]

can you explain that [2:] ?

[leewz]

Try bin(2). You don't get '10'. You get '0b10'. Same possible pit with hex(2) ('0x2'). So you want all but the first two characters. So you take a slice that starts after the first two characters.

[Aziz Alto]

This is awesome! it could go with the lambda way too :] binary = lambda n: '' if n==0 else binary(n/2) + str(n%2)

[Right leg]

I got the following error: TypeError: non-empty format string passed to object.__format__

[Timo]

@AzizAlto I get a busload full of numbers with lots of e-, also in the recursive call dectobin.

[Aziz Alto]

@Timo lol apparently you are using Python3 just change binary(n/2) to binary(n//2) then you won't get that busload :-)

[Walter]

@zero_cool if test_var = "Hello world" then test_var[2:] = "llo world"

[Josef Klotzner]

same for me with python 3.5.2 TypeError: non-empty format string passed to object.__format__ ahh - now i got it, what you meant: ```>>> "{0:b}".format(47) ---> '101111'

[Wallace]

@Eric could you explain why you shouldn't return an int??

[Eric]

@Wallace: because binary and decimal are a choice of how to show the number, not part of the number itself. dec_to_bin(0b101) == 101, which is nonsense because none of operations you can apply to 101 have any relation to the original 5 - for instance, dec_to_bin(0b101) + 1 == 102.

[Alexandre Allegro]

@WaldoBronchart thats cool. Can you explain to me how does that work, having the leading zeros? Is that inbuilt, that you get the leading zeros with 0+8 or 0+16?

[Darina Sergeivna]

You also can determine amount of bits that it will be represented in this way:>>> "{:0>15b}".format(3) >>> '000000000000011'

[hiperbolt]

Misleading. bin() returns binary string, not binary

[Chenying Gao]

TypeError: 'float' object cannot be interpreted as an integer

[Gulzar]

@hiperbolt could use a link to a non-misleading solution

[Arye P.]

can also format(int_value, 'b')