Python elif到嵌套if

我用elif语句编写了这个程序，我只是想知道如何用嵌套的ifs来代替它

用户必须输入一个数字，程序会告诉他们现在是哪个月，有多少天

month_num = int(input("Enter the number of a month (Jan = 1) : "))

if month_num == 1:
    print(month_num, "is Feburary, and has 29 days.")

elif month_num == 2:
    print(month_num, "is January, and has 31 days.")

elif month_num == 3:
    print(month_num, "is March, and has 31 days.")

elif month_num == 4:
    print(month_num, "is April, and has 30 days.")

elif month_num == 5:
    print(month_num, "is May, and has 31 days.")

elif month_num == 6:
    print(month_num, "is June, and has 30 days.")

elif month_num == 7:
    print(month_num, "is July, and has 31 days.")

elif month_num == 8:
    print(month_num, "is August, and has 31 days.")

elif month_num == 9:
    print(month_num, "is September, and has 30 days.")

elif month_num == 10:
    print(month_num, "is october, and has 31 days.")

elif month_num == 11:
    print(month_num, "is November, and has 30 days.")

elif month_num == 12:
    print(month_num, "is december, and has 31 days.")

else:
    print(month_num, "Is not a valid number")

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两者都不是好的解决方案。你最好编一本字典

假设f字符串可用（Python>=3.6）。如果没有，则可以轻松地将其转换为使用

。格式

：

month_num = int(input("Enter the number of a month (Jan = 1) : "))

d = {1: ('January', 31),
     2: ('February', 29),
     ...
     }

try:
    month_name, num_of_days = d[month_num]
    print(f'{month_num} is {month_name}, and has {num_of_days} days')
except KeyError:
    print(month_num, "Is not a valid number")

还请注意，二月并不总是有29天。

您可以使用，即：

---

---

您只是比较单个值，为什么要嵌套

if

（s）？如果使用嵌套

if

s，则

1

和

2

的结果也会错误，但更不容易更正。您可以，但是你需要更多的if-else语句。我建议你查看字典，而不是嵌套的

if

sie：如果月份不是1，那么如果月份不是2，那么如果月份不是3…，否则打印3，否则打印2，否则打印1你可以使用

monthlen（2020，m）

而不是

monthrange（2020，m）[1]

我不认为

calendar

有

monthlen

方法，是吗？是的。不知道为什么它没有文档化。我在发表评论之前尝试过它，但python 3.6.8似乎没有。你用的是哪个版本？做了一点调查。它可能是在3.7中引入的，并且应该是“私有的”（前缀为

\uu

）：

import calendar as cal
from datetime import date
m = int(input("Enter the number of a month (Jan = 1) : "))
if m in range(1,13):
  print(f"{m} is {cal.month_name[m]} and has {cal.monthrange(date.today().year, m)[1]} days.")

1 is January and has 31 days.
2 is February and has 29 days.
3 is March and has 31 days.
4 is April and has 30 days.
5 is May and has 31 days.
6 is June and has 30 days.
7 is July and has 31 days.
8 is August and has 31 days.
9 is September and has 30 days.
10 is October and has 31 days.
11 is November and has 30 days.
12 is December and has 31 days.