当输入无效时，如何停止 for 循环迭代？ （不允许使用 while 循环）- Python

Question

for i in range (0, 3): 
    
    print() # When iterates creates a space from last section
    
    raw_mark = int(input("What was student: " + str(student_id[i]) + "'s raw mark (0 - 100)?: "))
    
    days_late = int(input("How many days late was that student (0 - 5)?: "))
    
    penalty = (days_late * 5)
    
    final_mark = (raw_mark - penalty)

    # Selection for validation 
    
    if 0 <= raw_mark <= 100 and 0 <= days_late <= 5 and final_mark >= 40:
        
        print("Student ID:", str(student_id[i]))
        
        print() # Spacing for user readability
        
        print("Raw mark was:", str(raw_mark),"but due to the assignment being handed in",
              str(days_late),"days late, there is a penalty of:", str(penalty),"marks.")
        
        print()
        
        print("This means that the result is now:", final_mark,"(this was not a capped mark)")

         
        
    elif 0 <= raw_mark <= 100 and 0 <= days_late <= 5 and final_mark < 40: # Final mark was below 40 so mark must be capped
        
        print("Student ID:", str(student_id[i]))
        
        print()
        
        print("Raw mark was:", str(raw_mark),"but due to the assignment being handed in",
              str(days_late),"days late, there is a penalty of:", str(penalty),"marks.")
        
        print()
        
        print("Therefore, as your final mark has dipped below 40, we have capped your grade at 40 marks.")

        
    else:
        print("Error, please try again with applicable values")

在 else 中，我希望循环返回但没有将 i 迭代到下一个值，这样它就可以是无限的，直到输入所有 3 个有效输入......不能使用 while 循环，也不能放置 if - elif- else 在循环之外。 我也不能使用函数:(

Answer 1

尝试这样的事情。 您可以跟踪有效输入的数量，并且只有while达到目标数量后才停止循环（ while ）。

valid_inputs = 0

while valid_inputs <= 3:
   ...

   if ...:
      ...
   elif ...:
      ...
   else:
      # Immediately reset to the top of the while loop
      # Does not increment valid_inputs
      continue

   valid_inputs += 1

Answer 2

您可以将输入语句放在包含 try 块的 while 循环中。

for j in range(3): # or any other range
    try:
        raw_mark = int(input("What was student: " + str(student_id[i]) + "'s raw mark (0 - 100)?: "))

        days_late = int(input("How many days late was that student (0 - 5)?: "))
        break
    except:
        pass

Answer 3

如果你真的不能使用 while 循环......

def get_valid_input():
   user_input = input(...)
   valid = True
   if (...):  # Do your validation here
      valid = False

   if valid:
      return user_input
   else:
      return get_valid_input()

for i in range (0, 3): 
   input = get_valid_input()
   # Do what you need to do, basically your program from the question
   ...
   ...

这里还有一些额外的问题，因为如果您不断获得错误的输入值，您需要担心达到最大递归限制的可能性，但理想情况下get_valid_input应该只在您确定您有一些有效的东西时返回。

Answer 4

你可以让你的 for 循环表现得像一个 while 循环并让它永远运行并将你的 i 实现为一个计数器。 然后循环只有在它达到 3（或 2，以便您的索引不会改变）时才能终止，否则它会被设置回 0：

cnt_i = -1
for _ in iter(int, 1):
    cnt_i += 1
    if ...

    else:
        cnt_i = 0
    if cnt_i == 2:
        break

但说真的，无论什么原因不使用 while 循环，你都应该使用它。