[Tutor] How to convert an integer into a binary?

[Danny Yoo]

On Wed, 8 Aug 2001, Haiyang wrote:

> How can I convert an interger into a binary code in Python?

Good question!  By the way, going the other way around, from binary to an
integer, is very easy:

###
>>> int('111001', 2)
57
###

and might be useful later on.


[This message does NOT have an "answer" attached to it, but it gives hints
on one way to do the int->binary conversion.]


One thing to notice is that if a number is odd, then its binary (base-2)
representation will end with a '1'.  Here are a few examples:

###
>>> int('10101', 2)
21                    # is odd
>>> int('1010', 2)
10                    # is even
>>> int('101', 2)
5                     # is odd
>>> int('10', 2)
2                     # is even
>>> int('1', 2)
1
###

So if you have some number, then it's really easy to know about the last
digit: just check to see if the number's even or odd.  Knowing what the
rest of the digits look like might still be a mystery though.



The second thing that might be useful is to look again at the example
above, but this time staring at two things: the binary number itself, and
its integer equivalent:

integer    binary
-------    ------
    21     10101
    10      1010
    5        101
    2         10
    1          1



Take a look at it, and see if you can spot a pattern.  Here's another
interpreter example with a peculiar pattern:

###
>>> int('100110', 2)
38
>>> int('10011', 2)
19
>>> int('1001', 2)
9
>>> int('100', 2)
4
>>> int('10', 2)
2
>>> int('1', 2)
1
###


Forgive me: I'm being deliberately obscure here.  *grin* If you're
impatient, please feel free to ask again, and one of us can reply with
some example code.

Good luck to you!