little-things/alphabetseq

#!/usr/bin/env python3
import itertools
import sys


def decimal_to_alphabet(n: int, alphabet: str) -> str:
	if n == 0:
		return alphabet[0]
	base = len(alphabet)
	digits = []
	while n:
		digits.append(alphabet[n % base])
		n //= base
	return ''.join(digits[::-1])


def alphabet_to_decimal(s: str, alphabet: str) -> int:
	base = len(alphabet)
	l = len(s)
	return sum(alphabet.index(s[l - 1 - i]) * base ** i for i in range(l))


def test():
	assert alphabet_to_decimal('ff', '0123456789abcdef') == 255
	assert alphabet_to_decimal('100', '0123456789abcdef') == 256
	assert decimal_to_alphabet(255, '0123456789abcdef') == 'ff'
	assert decimal_to_alphabet(256, '0123456789abcdef') == '100'
	assert decimal_to_alphabet(0, '0123456789') == '0'


def convert_start_stop(s, alphabet):
	if ':' in s:
		valalphabet, value = s.split(':')
		if not valalphabet:
			valalphabet = '0123456789'
	else:
		valalphabet, value = alphabet, s
	return alphabet_to_decimal(value, valalphabet)


if __name__ == '__main__':
	if len(sys.argv) == 2 and sys.argv[1] == '--test':
		test()
	elif len(sys.argv) in (3, 4):
		if len(sys.argv) == 3:
			sys.argv.append(sys.argv[-1])
		alphabet = sys.argv[1]
		start, stop = map(lambda x: convert_start_stop(x, alphabet), sys.argv[2:])
		for i in range(start, stop + 1):
			try:
				sys.stdout.write(decimal_to_alphabet(i, alphabet) + '\n')
			except (BrokenPipeError, IOError):
				try:
					sys.stdout.close()
				except IOError:
					pass
				break
	else:
		print('Usage: alphabetseq ALPHABET START [STOP]', file = sys.stderr)
		print('Generates the sequence from START to STOP (inclusive) using ALPHABET', file = sys.stderr)
		print('If STOP is omitted, it defaults to START, effectively making this a simple base transformation', file = sys.stderr)
		print('START and STOP have values of the form [[VALALPHABET]:]VALUE.', file = sys.stderr)
		print('  In the [VALALPHABET]:VALUE form, VALUE is expressed in terms of VALALPHABET, which defaults to 0123456789 (i.e. decimal) if omitted.', file = sys.stderr)
		print('  In the VALUE form, it is converted using ALPHABET.', file = sys.stderr)
		sys.exit(1)