python - 为什么此日计数器会产生错误的结果？

Question

您好，我是 Python 初学者，目前在 PyCharm 上使用 Python 3.4.1。我最近做了一个项目，计算两个日期之间的天数，但是有两个问题。

def get_first_day():
    while True:
        try:
            print('First Date')
            day = int(input('Day:'))
            month = int(input('Month:'))
            year = int(input('Year:'))
            print(day, '/', month, '/', year)
            date = [day, month, year * 365]
            get_second_day(date)
        except ValueError:
            print('You were supposed to enter a date.')

 def get_second_day(date_1):
    while True:
       try:
           print('Second Date')
           day = int(input('Day:'))
           month = int(input('Month:'))
           year = int(input('Year:'))
           print(day, '/', month, '/', year)
           date = [day, month, year * 365]
           convert_dates_and_months(date_1, date)
       except ValueError:
           print('You were supposed to enter a date.')


def convert_dates_and_months(date_1, date_2):
    days_unfiltered = [date_1[0], date_2[0]]
    months_unfiltered = [date_1[1], date_2[1]]
    year = [date_1[2], date_2[2]]
    date_unfiltered = zip(days_unfiltered, months_unfiltered, year)
    for d, m, y in date_unfiltered:
        if m in [1, 3, 5, 7, 8, 10, 12]:
            a = 31
        elif m in [4, 6, 9, 11]:
            a = 30
        elif m in [2, 0] and int(y) % 4 is 0:
            a = 29
        else:
            a = 28
        m *= a
    days = list(filter(lambda x: 0 < x < (a + 1), days_unfiltered))
    months = list(filter(lambda x: 0 < x < 13, months_unfiltered))
    date_1 = [days[0], months[0], year[0]]
    date_2 = [days[1], months[1], year[1]]
    determine_date_displacement(date_1, date_2)


def determine_date_displacement(date_1, date_2):
    full_dates = zip(date_1, date_2)
    days = -1
    for k, v in full_dates:
        days += (int(v) - int(k))
    if days < 0:
        days *= -1
    print(days)


get_first_day()

第一个问题是计数器返回两个日期之间的天数不正确。第二个是 def get_second_day 由于某种原因在最后重复。我会告诉你我的意思:

First Date
Day:10
Month:09
Year:03
10 / 9 / 3

Second Date
Day:06
Month:06
Year:06
6 / 6 / 6

1087

Second Date
Day:

事实上，我知道从 2003 年 9 月 10 日到 2006 年 6 月 6 日之间正好有 1,000 天，但项目返回了 1,087 天。

如果有人能解释为什么这个项目返回了错误的数字，以及为什么它要求我在最后再次填写第二个日期，那就完美了。

由于这是我的第一个问题，而且我是 Python 的初学者，因此对于此问题中出现的任何奇怪的措辞/不良做法，我提前表示歉意。

Answer 1

问题 1:

您的闰年计算已关闭:

闰年是years % 4 == 0但仅限多年 year % 100 == 0除非他们也是year % 400 == 0 :

2004,2008,2012 : leap year (%4==0, not %100==0)
1700,1800,1900 : no leap year (%4 == 0 , % 100 == 0 but not %400 == 0)
1200,1600,2000 : leap years (* 1200 theor. b/c gregorian cal start)

问题 2:

在您的输入中，您将年份预乘 365，而不检查闰年 - 他们应该有 366 天，但得到了 365 天 - 这会导致在计算闰年的天数时缺少天数。

问题 3:

您遇到控制流问题:get_second_day()重复，因为你这样做:

get_first_date()
    while without end:
        do smth
        call get_second_date(..)
             while without end:
                 do smth 
                 call some calculation functions
                     that calc and print and return with None 
                 back in get_second_date(), no break, so back to the beginning
                 of its while and start over forever - you are TRAPPED

• 通过输入 break 来修复它之后convert_dates_and_months(date_1, date)里面get_second_day(..)

<小时/>

建议:

您可以通过减少 get_first_day() 之间的重复代码量来简化输入。和get_second_day() - 这遵循 DRY 原则(D不要R重复Y我们自己):

def getDate(text):
    while True:
        try:
            print(text)
            day = int(input('Day:'))
            month = int(input('Month:'))
            year = int(input('Year:'))
            print(day, '/', month, '/', year)
            return [day, month, year * 365]  # see Problem 2
        except ValueError:
            print('You were supposed to enter a date.')


def get_first_day():
    date1 = getDate("First Date")
    # rest of code omitted 

def get_second_day(date_1):
    date = getDate("Second Date")
    # rest of code omitted 

<小时/>

更好的解决方案是利用datetime and datettime-parsing ，特别是如果您想处理输入验证和闰年估计，您将需要更多的检查。

使用datetime模块会简化很多:

import datetime

def getDate(text):
    while True:
        try:
            print(text)
            day = int(input('Day:'))
            month = int(input('Month:'))
            year = int(input('Year (4 digits):'))
            print(day, '/', month, '/', year)

            # this will throw error on invalid dates: 
            # f.e. 66.22.2871 or even (29.2.1977) and user
            # gets a new chance to input something valid
            return datetime.datetime.strptime("{}.{}.{}".format(year,month,day),"%Y.%m.%d")
        except (ValueError,EOFError):
            print('You were supposed to enter a valid date.')


def get_first_day():
    return getDate("First Date")

def get_second_day():
    return getDate("Second Date")

# while True: # uncomment and indent next lines to loop endlessly
first = get_first_day()     # getDate("First Date") and getDate("Second Date") 
second = get_second_day()   # directly would be fine IMHO, no function needed
print( (second-first).days) 

输出:

First Date
Day:10
Month:9
Year (4 digits):2003
10 / 9 / 2003
Second Date
Day:6
Month:6
Year (4 digits):2006
6 / 6 / 2006
1000 

好读:How to debug small programs (#1) - 遵循它，至少可能会导致您遇到控制流问题。