用正则表达式补全日期，单数前面加0

Question

2021-1-1 补全为 2021-01-01

2022-12-1 补全为 2022-12-01

2018-6-12 补全为 2018-06-12

怎么用正则表达式，完成上面的操作呢？

import re

t1 = '2021-11-1'

t2 = '2021-12-1'

t3= '2021-6-12'

for i in [t1,t2,t3]:

    t4 = re.sub('-(?=[1-9][^0-9]?)', '-0', i)

    print(t4)
#输出如下
2021-011-01
2021-012-01
2021-06-012

Answer 1

import re
t1 = '2021-11-1'
t2 = '2021-12-1'
t3= '2021-6-12'
for i in [t1,t2,t3]:
    t4 = re.sub('-(?=[1-9]([^0-9]|$))', '-0', i)
    print(t4)