python 3.0 base64多次解码

import base64
stc=input("输入需要进行解码的BASE64码：\n")
def base64count(src):
    print("开始..")    
    num=0  
    try:
        
        while True :
            src = base64.decodestring(src.encode('utf-8'))
            src=src.decode('ascii')
            
            num=num+1
            print("解码中,第%d次" %(num))
            
    except Exception as e:
        
        print("结束")
        return src      


if __name__ == '__main__':
    print(base64count(stc))