如何提示输入直到日期格式和时间格式正确？

Question

我正在做一个活动策划，我想提示开始日期和结束日期。验证一直有效到开始日期和开始时间，但在结束日期和时间期间出现问题。当结束日期格式不正确时，不再提示结束日期，而是再次提示开始时间，结束时间也一样。

import datetime as dt

date_format = "%d-%m-%Y"
time_format = "%H:%M"
start_date = input("Please enter start date: ")
while True:
     try:
          dt.datetime.strptime(start_date, date_format)
          start_time = input("Please enter start time: ")
          try:
               dt.datetime.strptime(start_time, time_format)
               end_date = input("Please enter end date: ")
               try:
                    dt.datetime.strptime(end_date, date_format)
                    end_time = input("Please enter end time: ")
                    try:
                         dt.datetime.strptime(end_time, time_format)
                         print(start_date,start_time)
                         print(end_date,end_time)
                    except:
                         print("This is the incorrect time string format. It should be HH:MM")
               except:
                    print("This is the incorrect date string format. It should be DD-MM-YYYY")
          except:
               print("This is the incorrect time string format. It should be HH:MM")          
     except:
          print("This is the incorrect time string format. It should be DD-MM-YYYY")
          start_date = input("Please enter start date: ")

Answer 1

对每个提示使用 while-loop。

import datetime as dt

date_format = "%d-%m-%Y"
time_format = "%H:%M"

while True:
    start_date = input("Please enter start date: ")
    try:
        dt.datetime.strptime(start_date, date_format)
        break
    except:
        continue

while True:
    start_time = input("Please enter start time: ")
    try:
        dt.datetime.strptime(start_time, time_format)
        break
    except:
        continue

while True:
    end_date = input("Please enter end date: ")
    try:
        dt.datetime.strptime(end_date, date_format)
        break
    except:
        continue

while True:
    end_time = input("Please enter end time: ")
    try:
        dt.datetime.strptime(end_time, time_format)
        break
    except:
        continue

print(start_date, start_time)
print(end_date, end_time)

Answer 2

如果在执行过程中发生错误，一切都会在 while true 之后重新开始，即在 start_time

考虑使用简单的状态机：

def prompt_start_time():
  #get input, do something and validate format
  if input_validated: 
     next_state = "prompt_date"
     return start_time, next_state
   else:
     return None, "prompt_start_time"

def prompt_date():
  #do something and return prompt date
  if input_validated: 
     next_state = "end_date"
  else:
     next_state = "prompt_date"
  return start_date, next_state

def end_date():
  #...

state_machine = {"prompt_start_time": prompt__start_time, "prompt_date":prompt_date, "end_date": end_date}

while True:
  value, state = state_machine[current_state]()
  current_state = state

Answer 3

这是一种简洁的 Pythonic 方法：

import datetime as dt

date_format = "%d-%m-%Y"
time_format = "%H:%M"

def get_date(date_format, input_message):

    date = None

    while True:
        try:
            date = input(input_message)
            dt.datetime.strptime(date, date_format)
        except:
            print("This is the incorrect date string format. It should be DD-MM-YYYY")
            # Error! Return to the start of the loop
            continue
        else:
            # Success! Exit loop
            break

    return date


def get_time(time_format, input_message):

    time = None

    while True:
        try:
            time = input(input_message)
            dt.datetime.strptime(time, time_format)
            
        except:
            print("This is the incorrect time string format. It should be HH:MM")
            # Error! Return to the start of the loop
            continue
        else:
            # Success! Exit loop
            break

    return time


start_date = get_date(date_format, "Please enter start date: ")
start_time = get_time(time_format, "Please enter start time: ")
end_date = get_date(date_format, "Please enter end date: ")
end_time = get_time(time_format, "Please enter end time: ")

我们创建了 2 个函数：一个用于日期输入，另一个用于时间输入
然后我们通过更改作为参数传递的输入消息来调用这些函数

输入验证逻辑包含在2个函数中，这样代码维护起来会更容易。

关于如何输入验证的说明已完成：这里我们使用 try/except/else:

如果 try 子句引发异常，它将执行 except
中的内容
如果try子句没有抛出异常，就会执行else
中的代码
if in except: we are here because input is wrong, so we print a message, and we use continue order to go directly at the start of the loop, in命令再次执行try中的代码。
如果我们在else：输入OK，所以我们使用break以便离开while循环。

如何提示输入直到日期格式和时间格式正确？

How to prompt input until date format and time format is correct?

python

try-except