How to convert decimal to binary list in python

Question

Possible Duplicate:
Convert an integer to binary without using the built-in bin function

how do I convert a decimal number into a binary list.

For example, how do I change 8 into [1,0,0,0]

I tried this: binary = 0 while num != 0: bit = num % 2 binary = bit +(10* binary) num = num / 2 binary=[binary] return binary but it doesn't give me commas between the numbers, and it doesn't always add the zeros. — booboboobobob, Nov 26 '12 at 02:39
What have you tried? You might want to look at the python docs for the function `bin`. — Yuushi, Nov 26 '12 at 02:39
[This question](http://stackoverflow.com/questions/13522773/convert-an-integer-to-binary-without-using-the-built-in-bin-function) has already been asked. — John, Nov 26 '12 at 02:40
@booboboobobob You should put such constraints in your question then. — Yuushi, Nov 26 '12 at 02:40
@mgilson, I flagged it as an exact duplicate... should I have voted to close instead? — John, Nov 26 '12 at 02:59
@johnthexiii -- See [this post on meta](http://meta.stackexchange.com/a/91839/190459) — mgilson, Nov 26 '12 at 03:02
@mgilson, I will start doing that once I have the 3K rep, +1 thanks for the link. — John, Nov 26 '12 at 03:08
@johnthexiii -- I couldn't remember how much rep was required for that. Thanks for finding the duplicate. — mgilson, Nov 26 '12 at 03:09

score 31 · Answer 1 · answered Nov 26 '12 at 02:39

31

You can probably use the builtin bin function:

bin(8) #'0b1000'

to get the list:

[int(x) for x in bin(8)[2:]]

Although it seems like there's probably a better way...

answered Nov 26 '12 at 02:39

mgilson

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Relying on string representation details and going from an integer to a string and then to a list seems....suboptimal. – slacy Feb 10 '17 at 23:56

Sean Redmond · Answer 2 · 2012-11-26T02:55:56.607

Try this:

>>> list('{0:0b}'.format(8))
['1', '0', '0', '0']

Edit -- Ooops, you wanted integers:

>>> [int(x) for x in list('{0:0b}'.format(8))]
[1, 0, 0, 0]

Another edit --

mgilson's version is a little bit faster:

$ python -m timeit "[int(x) for x in list('{0:0b}'.format(8))]"
100000 loops, best of 3: 5.37 usec per loop
$ python -m timeit "[int(x) for x in bin(8)[2:]]"
100000 loops, best of 3: 4.26 usec per loop

score 7 · Answer 3 · answered Nov 26 '12 at 02:46

7

In the spirit of your original attempt:

binary = []
while num != 0:
    bit = num % 2
    binary.insert(0, bit)
    num = num / 2

answered Nov 26 '12 at 02:46

Alexey Feldgendler

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Would be better to `.append()` the bits then `.reverse()` the list at the end rather than `insert`ing at the start of the list. – Tim Nov 26 '12 at 02:58

How to convert decimal to binary list in python

3 Answers3