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How to convert an integer to a string in any base?

Asked 2010-02-15T16:33:01.440
350

Python allows easy creation of an integer from a string of a given base via 

int(str, base).

I want to perform the inverse: creation of a string from an integer, i.e. I want some function int2base(num, base), such that:

int(int2base(x, b), b) == x

The function name/argument order is unimportant.

For any number x and base b that int() will accept.

This is an easy function to write: in fact it's easier than describing it in this question. However, I feel like I must be missing something.

I know about the functions bin, oct, hex, but I cannot use them for a few reasons:

  • Those functions are not available on older versions of Python, with which I need compatibility with (2.2)

  • I want a general solution that can be called the same way for different bases

  • I want to allow bases other than 2, 8, 16

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python radix
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2 Answers

107
def baseN(num,b,numerals="0123456789abcdefghijklmnopqrstuvwxyz"):
    return ((num == 0) and numerals[0]) or (baseN(num // b, b, numerals).lstrip(numerals[0]) + numerals[num % b])

ref: http://code.activestate.com/recipes/65212/

Please be aware that this may lead to

RuntimeError: maximum recursion depth exceeded in cmp

for very big integers.

answered 2010-02-15T16:41:46.863
15

You could use baseconv.py from my project: https://github.com/semente/python-baseconv

Sample usage:

>>> from baseconv import BaseConverter
>>> base20 = BaseConverter('0123456789abcdefghij')
>>> base20.encode(1234)
'31e'
>>> base20.decode('31e')
'1234'
>>> base20.encode(-1234)
'-31e'
>>> base20.decode('-31e')
'-1234'
>>> base11 = BaseConverter('0123456789-', sign='$')
>>> base11.encode('$1234')
'$-22'
>>> base11.decode('$-22')
'$1234'

There is some bultin converters as for example baseconv.base2, baseconv.base16 and baseconv.base64.

answered 2012-09-25T20:42:40.047

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