base64编码-Python

# base64解码
class Decoder(object):
	tables = None 
	def __init__(self):
		self.__generateCodeTable()
	def __generateCodeTable(self):
		"""
		解码的码表
		"""
		codeTable = {}
		# ord(ss) 输出字符的ascii
		# chr(num) 输出数值对应的字符
		init_char = ord('A') - 1
		for i in range(26):
			init_char = chr(init_char + 1)
			codeTable[init_char] = i
		init_char = ord('a') - 1
		for j in range(26,52):
			init_char = chr(init_char + 1)
			codeTable[init_char] = j
		init_char = ord('0') -1
		for k in range(52,62):
			init_char = chr(init_char + 1)
			codeTable[init_char] = k
		codeTable['+'] = 62
		codeTable['/'] = 63
		self.tables = codeTable
	def __characterTo6Bin(self,msg):
		"""
		将每个字符串转化为6位的二进制
		"""
		result = ''
		for i in range(len(msg)):
		 	tep_str = ''
		 	tmp = bin(self.tables.get(msg[i]))[2:]
		 	if len(tmp) < 6 :
		 		num = 6 - len(tmp)
		 		for j in range(num):
		 			tep_str += '0'
		 	tep_str += tmp
		 	result += tep_str
		return result
	def decode(self,msg):
		"""
		解码base64编码的字符
		"""
		index = msg.find('=')
		if index != -1:
			msg = msg[0:index]
		result = []
		str_bin = self.__characterTo6Bin(msg)
		length = len(str_bin)
		index = 0
		while index < length:
			if int(str_bin[index:index+8],2) > 127:
				tmp = str_bin[index:index+24]
				hex_str = str(hex(int(tmp,2)))
				hex_str = hex_str.replace('0x','')
				result.append(str(bytes.fromhex(hex_str),encoding='utf-8'))
				index += 24
			else:
				sub = str_bin[index:index+8]
				result.append(chr(int(sub,2)))
				index += 8
		if result[-1] == 0:
			result = result[0:-1]
		origin = ""
		for key in result:
			origin += key
		return origin.replace('\x00','')
decode = Decoder()
decode.decode('5Lit5Zu9')