Base converter

BaseConv.py

from collections import OrderedDict

class BaseConv:
    def __init__(self, charset:str):
        self.charset = OrderedDict.fromkeys(charset)
        i = 0
        for k in self.charset:
            self.charset[k] = i
            i += 1
        self.charset_string = ''.join(self.charset.keys())
        self.base_count = len(self.charset)

    def fromdec(self, num:int) -> str:
        s = ""
        while num > 0:
            index = num % self.base_count
            s = self.charset_string[index] + s
            num = (num - index) // self.base_count
        return s

    def todec(self, s:str) -> int:
        sanitized = ''.join(x for x in s if x in self.charset)
        slen = len(sanitized)
        num = 0
        for i in range(slen):
            num += self.charset[sanitized[i]] * (self.base_count ** (slen - i - 1))
        return num

class Coding:
    def __init__(self, frombase:BaseConv, tobase:BaseConv):
        self.frombase = frombase
        self.tobase = tobase

    def encode(self, fromstr: str) -> str:
        return self.tobase.fromdec(self.frombase.todec(fromstr))

    def decode(self, fromstr: str) -> str:
        return self.frombase.fromdec(self.tobase.todec(fromstr))

test.py

from BaseConv import BaseConv, Coding
b64str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
asciistr = ''.join(chr(i) for i in range(256))
b64 = BaseConv(b64str)
ascii = BaseConv(asciistr)
s = "Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure. "

c = Coding(ascii, b64)
print(c.encode(s))
print(c.decode(c.encode(s)))