from python_toolbox import sequence_tools

class NumberEncoder:

def __init__(self, characters):

self.characters = \

sequence_tools.ensure_iterable_is_immutable_sequence(characters)

recurrences = sequence_tools.get_recurrences(self.characters)

if recurrences:

raise Exception('`characters` must not have recurring characters.')

def encode(number, minimum_length=1):

current_number = number

result = ''

while current_number:

current_number, modulo = divmod(current_number,

len(self.characters))

result = self.characters[modulo] + result

if len(result) <= minimum_length:

result = (self.characters[0] * (minimum_length - len(result))) + result

return result

def decode(self, string):

assert isinstance(string, (str, bytes))

return sum((len(self.characters)**i) * self.characters.index(x)

for (i, x) in enumerate(string[::-1]))