Python中的模算术计算错误

Question

我有以下代码，其中一个特定的条目组合出现了一个神秘的错误：

除了输入“Friday”和“1000”之外，它*似乎“可以正常工作，它会引发变量错误。

完整代码清单： https://repl.it/Jd6a/0

代码

#Use of Modulo Arithmetic

def main():
  DAY="Monday"
  print("Here's a little modulo magic for ya...")
  dayofweek=input("Enter day of week (e.g. Monday, Tuesday, Wednesday, etc:")
  numberofdays=input("Enter number of days from that day of the week you would like to calculate:")

  if dayofweek=="Monday":
    dow=1 
  elif dayofweek=="Tuesday":
    dow=2 
  elif dayofweek=="Wednesday":
    dow=3 
  elif dayofweek=="Thursday":
    dow=4 
  elif dayofweek=="Friday":
    dow=5 
  elif dayofweek=="Saturday":
    dow=6 
  elif dayofweek=="Sunday":
    dow=7 

  modanswer=int(numberofdays)%7
  answer=modanswer+dow

  if answer==1:
    finalanswer="Monday"
  elif answer==2:
    finalanswer="Tuesday"
  elif answer==3:
    finalanswer="Wednesday"
  elif answer==4:
    finalanswer="Thursday"
  elif answer==5:
    finalanswer="Friday"
  elif answer==6:
    finalanswer="Saturday"
  elif answer==7:
    finalanswer="Sunday"

  print(numberofdays,"days from -",dayofweek,"-will be-",finalanswer)

main()

测试（正确）和错误如下所示

Here's a little modulo magic for ya...
Enter day of week (e.g. Monday, Tuesday, Wednesday, etc: Monday
Enter number of days from that day of the week you would like to calculate: 1000000
1000000 days from - Monday -will be- Tuesday
   main()
Here's a little modulo magic for ya...
Enter day of week (e.g. Monday, Tuesday, Wednesday, etc: Friday
Enter number of days from that day of the week you would like to calculate: 1000
Traceback (most recent call last):
  File "python", line 1, in <module>
  File "python", line 42, in main
UnboundLocalError: local variable 'finalanswer' referenced before assignment

我在寻找什么：

我对 a) 对问题进行解释的解决方案感兴趣 b) 更优雅的方法，通过验证来解决问题（也许使用更简单的构造）

Answer 1

 modanswer=int(numberofdays)%7
 answer=modanswer+dow

modanwer 介于 0 和 6（含）之间，dow 介于 1 和 7（含）之间，因此 answer 介于 0 和 13（含）之间。您应该在加法后应用模运算。这可能有效：

answer = (int(numberofdays) + dow - 1) % 7 +1

-1 和 +1 是必需的，因为您的 answer 介于 1 和 7 之间，但取模返回一个介于 0 和 6 之间的数字。

您可以简单地使用列表、0-index day_number 和模数：

days = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']

day_number = days.index('Friday') # 4
offset = 1000
print(days[(day_number + offset) % 7])
# Thursday