日期时间模块Python

我正在试验Python中的Datetime模块，并决定制作一个向前和向后计算天数的程序。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)

我发现了错误

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'

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不能从日期时间中减去字符串。首先尝试将其转换为时间增量。

不能从日期时间中减去字符串。首先尝试将其转换为时间增量。

使用，您需要：

使用，您需要：

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代码的其余部分在哪里？很好，您将代码减少到了大部分-，但它不是完全自一致的，这使得一致性回答有点困难。代码的其余部分在哪里？很好，您将代码减少到了大部分-，但它不是完全自一致的，这使得一致性回答有点困难。

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)
...

>>> 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)