字符串逆序[Python]

str = 'yob a ma i' # 10


def recursion(mystr):
    global rstr
    index = 0
    strlen = len(mystr)
    
    if 1 != strlen:
        recursion(mystr[index+1:strlen])
    print  mystr[index]
    rstr += mystr[index]
    
    
rstr= '' 
recursion(str) 
print rstr