本文利用Python计算今天日期、明天日期、和昨天日期的相关方法，及获取当前日期是星期几。

python编程操作日期时间主要用到的python模块是datetime和time这2个模块

获取星期几from datetime import datetime, date

dayOfWeek = datetime.now().weekday()

print(dayOfWeek)

dayOfWeek = datetime.today().weekday()

print(dayOfWeek)

注意：datetime类的weekday()方法可以获得datetime是星期几，注意weekday()返回的是0~6，是星期一到星期日。

python获取今日日期import datetime

today = datetime.date.today()

print(today)

输出：2019-06-25

python获取昨日日期import datetime

today = datetime.date.today()

zuotian = today- datetime.timedelta(days=1)

print(zuotian)

获取明天日期import datetime

today = datetime.date.today()

tomorrow = today + datetime.timedelta(days=1)

print(tomorrow)

获取后天日期import datetime

today = datetime.date.today()

tomorrow = today + datetime.timedelta(days=2)

print(tomorrow)

小结：不管是往前计算还是往后计算，直接在今日日期上进行天数的相加减

def date_to_week(year,month,day):
    if year<1990:a=max(1990,year)
    else:a=max(1990,year)+1
    b,count_day=min(1990,year),day
    for j in range(b,a):
        if j % 4 == 0 and j% 100 != 0 or j % 400 == 0:two = 29
        else:two = 28
        list_month=[31,two,31,30,31,30,31,31,30,31,30,31]
        if  year<1990 and j==year:count_day=sum(list_month[:month-1:-1])+list_month[month-1]-count_day
        else:
            if j < a and j != year:mm = 13
            else:mm = month
            count_day += sum(list_month[:mm - 1])
        if j == 1989: count_day = -count_day
    week_day=['日','一','二','三','四','五','六']
    index=count_day%7
    return '星期{}'.format(week_day[index])

以上是编程代码，此处是使用1990.1.1为基准日，基准日可以随便定义，但是一定要知道定义的基准日是星期几。通过判断闰年来确定2月的天数，从而确定该年份是多少天，与基准日求差值，大于基准日选择正值，小于选择负值，再用对应的差值对7求余，剩的余数就是对应周列表的索引。