用python进行月份加减的函数

import mathdef add_month(datamonth, num):
"""
月份加减函数,返回字符串类型
:param datamonth: 时间(201501)
:param num: 要加(减)的月份数量
:return: 时间(str)
"""
months = ['', '', '', '', '', '', '', '', '', '', '', '']
datamonth = int(datamonth)
num = int(num)
year = datamonth // 100
new_list = []
s = math.ceil(abs(num) / 12)
for i in range(int(-s), s + 1):
new_list += [str(year + i) + x for x in months]
new_list = [int(x) for x in new_list]
return str(new_list[new_list.index(datamonth) + num])if __name__ == '__main__':
a = add_month('', 5)
print(a)