Conversion between different bases in Python (binary octal decimal and hexadecimal)

In my mind, conversion between bases is a very common problem, so in Python, the following code is also included as util.

This is an Python conversion from a web search that is still working, and it is verified to work. The code for its implementation is posted below:

#!/usr/bin/env python 
# -*- coding: utf-8 -*- 
# 2/10/16 base trans. wrote by srcdog on 20th, April, 2009 
# ld elements in base 2, 10, 16. 
 
import os,sys 
 
# global definition 
# base = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F] 
base = [str(x) for x in range(10)] + [ chr(x) for x in range(ord('A'),ord('A')+6)] 
 
# bin2dec 
#  binary  to  The decimal system : int(str,n=10)  
def bin2dec(string_num): 
  return str(int(string_num, 2)) 
 
# hex2dec 
#  hexadecimal  to  The decimal system  
def hex2dec(string_num): 
  return str(int(string_num.upper(), 16)) 
 
# dec2bin 
#  The decimal system  to  binary : bin()  
def dec2bin(string_num): 
  num = int(string_num) 
  mid = [] 
  while True: 
    if num == 0: break 
    num,rem = divmod(num, 2) 
    mid.append(base[rem]) 
 
  return ''.join([str(x) for x in mid[::-1]]) 
 
# dec2hex 
#  The decimal system  to  octal : oct()  
#  The decimal system  to  hexadecimal : hex()  
def dec2hex(string_num): 
  num = int(string_num) 
  mid = [] 
  while True: 
    if num == 0: break 
    num,rem = divmod(num, 16) 
    mid.append(base[rem]) 
 
  return ''.join([str(x) for x in mid[::-1]]) 
 
# hex2tobin 
#  hexadecimal  to  binary : bin(int(str,16))  
def hex2bin(string_num): 
  return dec2bin(hex2dec(string_num.upper())) 
 
# bin2hex 
#  binary  to  hexadecimal : hex(int(str,2))  
def bin2hex(string_num): 
  return dec2hex(bin2dec(string_num))