日期时间模块Python

Question

我正在试用Python中的Datetime模块，并决定制作一个程序来向前和向后计算天数。相关代码：

if bORf == 'f':
    howfarforward = input("How far forward would you like to count?: ")
    def countforward(howfarfor):
        day = datetime.date.today()
        day -= howfarfor
        print(day)
    countback(howfarfor)

我得到了错误

^{pr2}$

我知道为什么，我只是不知道怎么解决它。我该怎么做？在

其余代码：

import datetime
print("Today is", datetime.date.today())
bORf = input("Would you like to count backwards or forwards? (b/f)")
if bORf == 'b':
    howfarback = input("How far back would you like to count?: ")
        def countback(howfarback):
            day = datetime.date.today()
            day -= howfarback
            print(day)
        countback(howfarback)
...

Answer 1

使用^{}，您需要parse the ^{} to a number：

>>> import datetime
>>> howfarforward = int(input("How far forward would you like to count?: "))
How far forward would you like to count?: 4
>>> day = datetime.date.today()
>>> day = day + datetime.timedelta(days=howfarforward)
>>> day
datetime.date(2012, 3, 18)

Answer 2

不能从日期时间中减去字符串。先把它转换成timedelta。在