def str1(list1):
    c="".join(map(str,list1))
    return c    
a=[1, 2, 3, 4, 5, 6, 7, 8, 9]
print(str1(a))

#方法二
def str2(list2):
    d=0
    for i in list2:
        d=d*10+i
    return d
a=[1, 2, 3, 4, 5, 6, 7, 8, 9]
print(str2(a))

#方法三：高阶函数
from functools import reduce
def Change_list(list):
    def fn(x,y):
        return x*10+y    
    return reduce(fn,list)
a=[1, 2, 3, 4, 5, 6, 7, 8, 9]
print(Change_list(a))