code: def base64_decode(data):
      
      data = data.replace(__enc64__[64], '')
      total = len(data)
      result = []
      mod = 0
      for i in range(total):
          mod = i % 4
          cur = __enc64__.index(data[i])
          if mod == 0:
              continue
          elif mod == 1:
              prev = __enc64__.index(data[i - 1])
              result.append(chr(prev << 2 | cur >> 4))
          elif mod == 2:
              prev = __enc64__.index(data[i - 1])
              result.append(chr((prev & 0x0f) << 4 | cur >> 2))
          elif mod == 3:
              prev = __enc64__.index(data[i - 1])
              result.append(chr((prev & 3) << 6 | cur))
  
      return "".join(result)
docs: Base 64 decoder