主要用到两个库，time和datetime

import time
import datetime
import re


# 格式化日期字符串


def formatDateStr(date_string, target_pattern='%Y-%m-%d'):
    # 日期格式转换(yyyy-MM-dd HH:mm:ss,yyyy/MM/dd,yyyyMMdd
    patterns = {'%Y-%m-%d %H:%M:%S': '\d{4}-[01]\d-[0123]\d\s{1,2}[012]\d:[0-5]\d:[0-5]\d',
                '%Y/%m/%d': '\d{4}/[01]\d/[0123]\d',
                '%Y%m%d': '\d{4}[01]\d[0123]\d'}
    for key, value in patterns.items():
        if re.match(value, date_string, re.M | re.I):
            # 字符转换为tuple
            time_tuple = time.strptime(date_string, key)
            # tuple转化为字符串
            return time.strftime(target_pattern, time_tuple)
        else:
            pass
    return ''


def formatDateStr2(date_string, target_pattern='%Y-%m-%d'):
    # 日期格式转换(yyyy-MM-dd HH:mm:ss,yyyy/MM/dd,yyyyMMdd
    patterns = {'%Y-%m-%d %H:%M:%S': '\d{4}-[01]\d-[0123]\d\s{1,2}[012]\d:[0-5]\d:[0-5]\d',
                '%Y/%m/%d': '\d{4}/[01]\d/[0123]\d',
                '%Y%m%d': '\d{4}[01]\d[0123]\d'}
    for key, value in patterns.items():
        if re.match(value, date_string, re.M | re.I):
            # 字符转换为time
            date = datetime.datetime.strptime(date_string, key)
            # 获取年
            year = datetime.datetime.strptime(date_string, key).year
           # 获取月
            month = datetime.datetime.strptime(date_string, key).month
           # 获取日
            day = datetime.datetime.strptime(date_string, key).day
            return date.strftime(target_pattern)
        else:
            pass
    return ''


def formatTimeStr(time_str, target_pattern='%H:%M:%S'):
    patterns = {'%H:%M:%S': '[012]\d:[0-5]\d:[0-5]\d', '%H%M%S': '[012]\d[0-5]\d[0-5]\d'}
    for key, value in patterns.items():
        if re.match(value, time_str, re.M | re.I):
            # 字符转换为tuple
            time_tuple = time.strptime(time_str, key)
            # tuple转化为字符串
            return time.strftime(target_pattern, time_tuple)
        else:
            pass
    return time_str

# 计算两个时间段的天数
def formatCycleTime(date_string):
    # 日期格式转化2019.01.18-2019.03.15
    patterns = {'%Y.%m.%d-%Y.%m.%d': '\d{4}\.[01]\d\.[0123]\d-\d{4}\.[01]\d\.[0123]\d',
                '%Y/%m/%d-%Y/%m/%d': '\d{4}\/[01]\d\/[0123]\d-\d{4}\/[01]\d\/[0123]\d'}
    for key, value in patterns.items():
        if re.match(value, date_string, re.M | re.I):
            dates = date_string.split('-')
            startDate = dates[0]
            endDate = dates[1]
            d1 = datetime.datetime.strptime(startDate, key.split('-')[0])
            d2 = datetime.datetime.strptime(endDate, key.split('-')[0])
            return (d2 - d1).days
    return ''


def parseTimeStamp2Date(timestamp):
    # 时间戳转化为time
    return time.localtime(timestamp)

def parseDate2TimeStamp(time_tuple):
    # 转化为时间戳
    return time.mktime(time_tuple)


if __name__ == '__main__':
    str = '2019-08-29 23:59:49'
    print(formatDateStr(str))
    print(formatDateStr2(str))

运行结果：

时间字符串格式化