python - 日期时间模块 Python

Question

我正在 Python 中试验 Datetime 模块，并决定制作一个程序来计算前后的天数。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)

我遇到了错误

Traceback (most recent call last):
  File "datecount.py", line 11, in <module>
    countback(howfarback)
  File "datecount.py", line 9, in countback
    day -= howfarback
TypeError: unsupported operand type(s) for -=: 'datetime.date' and 'str'

我知道为什么，只是不知道如何解决。我该怎么做？

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datetime.timedelta , 你需要 parse the input 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)