Encode/decode an incrementing integers as an alphanumeric identifier

identifier.py

"""
Encode/decode an incrementing integers as an alphanumeric identifier.
Uses digits and case-insensitive letters (produces caps, accepts both), minimum length 3.
Does not cryptographically hide the original id.
"""

def to_code(nr):
	assert nr >= 0
	nr *= 7
	code = ''
	while nr > 0:
		letter = ALPHABET[nr % len(ALPHABET)]
		code = letter + code
		nr //= len(ALPHABET)
	while len(code) < 3:
		code = ALPHABET[0] + code
	return code


def from_code(code):
	code = code.upper()
	nr = 0
	mult = 1
	for letter in reversed(code):
		nr += mult * REVERSE_ALPHABET[letter]
		mult *= len(ALPHABET)
	assert nr % 7 == 0
	return nr // 7