python 递归处理多重嵌套list

a = [1,'Dave',3.14,["Mark",7,9,[100,101]],10]
def foo(arr):
    lit = ''
    for i in arr:
        if isinstance(i,list):
            lit += foo(i)
        else:
            lit += str(i) + "-"
    return  lit
str1 = foo(a)
print str1[0:-1].split('-')