Python base 36 encoding

Question

How can I encode an integer with base 36 in Python and then decode it again?

Answer 1

I wish I had read this before. Here is the answer:

def base36encode(number):
    if not isinstance(number, (int, long)):
        raise TypeError('number must be an integer')
    if number < 0:
        raise ValueError('number must be positive')

    alphabet, base36 = ['0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ', '']

    while number:
        number, i = divmod(number, 36)
        base36 = alphabet[i] + base36

    return base36 or alphabet[0]


def base36decode(number):
    return int(number, 36)

print(base36encode(1412823931503067241))
print(base36decode('AQF8AA0006EH'))

Answer 2

You can use numpy's base_repr(...) for this.

import numpy as np

num = 2017

num = np.base_repr(num, 36)
print(num)  # 1K1

num = int(num, 36)
print(num)  # 2017

Here is some information about numpy, int(x, base=10), and np.base_repr(number, base=2, padding=0).

(This answer was originally submitted as an edit to @christopher-beland's answer, but was rejected in favor of its own answer.)

Answer 3

Have you tried Wikipedia's sample code?

def base36encode(number, alphabet='0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
    """Converts an integer to a base36 string."""
    if not isinstance(number, (int, long)):
        raise TypeError('number must be an integer')

    base36 = ''
    sign = ''

    if number < 0:
        sign = '-'
        number = -number

    if 0 <= number < len(alphabet):
        return sign + alphabet[number]

    while number != 0:
        number, i = divmod(number, len(alphabet))
        base36 = alphabet[i] + base36

    return sign + base36

def base36decode(number):
    return int(number, 36)

print base36encode(1412823931503067241)
print base36decode('AQF8AA0006EH')

Answer 4

This works if you only care about positive integers.

def int_to_base36(num):
    """Converts a positive integer into a base36 string."""
    assert num >= 0
    digits = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'

    res = ''
    while not res or num > 0:
        num, i = divmod(num, 36)
        res = digits[i] + res
    return res

To convert back to int, just use int(num, 36). For a conversion of arbitrary bases see https://gist.github.com/mbarkhau/1b918cb3b4a2bdaf841c

Answer 5

I benchmarked the example encoders provided in answers to this question. On my Ubuntu 18.10 laptop, Python 3.7, Jupyter, the %%timeit magic command, and the integer 4242424242424242 as the input, I got these results:

• Wikipedia's sample code: 4.87 µs ± 300 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
• @mistero's base36encode(): 3.62 µs ± 44.2 ns per loop
• @user1036542's int2base: 10 µs ± 400 ns per loop (after fixing py37 compatibility)
• @mbarkhau's int_to_base36(): 3.83 µs ± 28.8 ns per loop

All timings were mean ± std. dev. of 7 runs, 100000 loops each.

Answer 6

You could use https://github.com/tonyseek/python-base36.

$ pip install base36

and then

>>> import base36
>>> assert base36.dumps(19930503) == 'bv6h3'
>>> assert base36.loads('bv6h3') == 19930503