任务是：清理不同日期格式的日期（如3/14/2019，03-14-2019和2015/3/19），将其替换为单一标准格式的日期。
不知道怎么完成

import re

text = "3/14/2019, 03-14-2019, and 2015/3/19"

datePtn = re.compile(r"""(
(\d{1,4}) #group 1
(-|/|\.) #separator group 2
(\d{1,2}) #group 3
(-|/|\.) #separator group 4
(\d{1,4}) #group 5
)""",re.VERBOSE)

matches = []
findallResult = datePtn.findall(text)
for group in findallResult:
    if len(group[1]) > 2:
        dateNew = '/'.join([group[3],group[5],group[1]])
        matches.append(dateNew)
    else:
        dateNew = '/'.join([group[1],group[3],group[5]])
        matches.append(dateNew)

newDates = []
month = ''
day = ''
for date in matches:
    for group in datePtn.findall(date): #group is tuple
        if group[1][0] == "0":
            month = group[1][1]
        else:
            month = group[1]
        if group[3][0] == '0':
            day = group[3][1]
        else:
            day = group[3]
        newDate = '/'.join([month,day,group[5]])
        newDates.append(newDate)
print("new dates")
print(newDates)

oldDates = []
for i in findallResult:
    oldDates.append(i[0])
print("old dates")
print(oldDates)

字符串
我可以得到两个名单与旧的和新的日期。如何创建一个只替换日期的字符串？谢谢你的好意