当键不在字典中时如何使用异常处理进行for循环？

Question

所以，我有一本包含国家名称和相应股票指数的字典。用户被要求输入五个不同的国家，程序获取五个相应的股票指数并对数据进行处理。

当被要求输入时，我检查字典是否可以找到该国家/地区，这种情况发生了五次。现在，处理异常的部分没有做我希望的事情。我的循环和/或异常处理有什么问题？？

ex_dict = {'United States': '^GSPC','United States of America': '^GSPC', 'Usa': '^GSPC', 'Argentina': '^MERV'} #shortened on purpose

countries = []
print('Please choose five stock exchanges to analyse,' )
print('just name the corresponding countries \n')

for i in range(0, 5):
    while True:
        try:
            countr = input('Please enter country no. %d: ' %(i+1))
            countr = countr.title()            
            if countr in ex_dict.keys():
                print('Found the corresponding stock index! \n')
                countries.append(countr)
            break
        except KeyError:
            print('Country not found, please try again! \n')

Answer 1

几点：

• 您的代码永远不会遇到异常，因为您正在使用 if key in dict.keys() 检查密钥是否存在

• 此外，还有很多循环。我认为for i in range(0,5) 就足够了。会不那么复杂。

  ex_dict = {'United States': '^GSPC','United States of America': '^GSPC', 'Usa': '^GSPC', 'Argentina': '^MERV'} #shortened on purpose
  
  countries = []
  print('Please choose five stock exchanges to analyse,' )
  print('just name the corresponding countries \n')
  
  for i in range(0, 5):
      countr = raw_input('Please enter country no. %d: ' %(i+1))
      countr = countr.title()
      if countr in ex_dict.keys():
          print('Found the corresponding stock index! \n')
          countries.append(countr)
      else:
          print('Country not found, please try again! \n')
  

输出：

C:\Users\dinesh_pundkar\Desktop>python c.py
Please choose five stock exchanges to analyse,
just name the corresponding countries

Please enter country no. 1: USA
Found the corresponding stock index!

Please enter country no. 2: asd
Country not found, please try again!

Please enter country no. 3: asd
Country not found, please try again!

Please enter country no. 4: USA
Found the corresponding stock index!

Please enter country no. 5: United states
Found the corresponding stock index!


C:\Users\dinesh_pundkar\Desktop>

Answer 2

如果股票不在字典 ex_dict 中，我假设你希望它给你一个消息，我已经修改了代码来做同样的事情。

ex_dict = {'United States': '^GSPC','United States of America': '^GSPC', 'Usa': '^GSPC', 'Argentina': '^MERV'} #shortened on purpose

countries = []
print('Please choose five stock exchanges to analyse,' )
print('just name the corresponding countries \n')

for i in range(0, 5):
    while True:
        try:
            countr = input('Please enter country no. %d: ' %(i+1))
            countr = countr.title()            
            if countr not in ex_dict.keys():
                print ('Try again!')
            else:
                print('Found the corresponding stock index! \n')
                countries.append(countr)

Answer 3

来自doc

每当请求 dict() 对象（使用格式 a = adict[key]）并且键不在字典中时，Python 都会引发 KeyError。

如果您想在用户插入国家/地区字典中不存在的键时打印一条消息，则在您的代码中，您可以简单地添加一个 else 语句而不是 catch 异常。

您可以通过这种方式更改您的代码：

if countr in ex_dict.keys():
     print('Found the corresponding stock index! \n')
     countries.append(countr)
     break
else:
    print('Country not found, please try again! \n')

Answer 4

这里不会有KeyError，因为您的代码永远不会厌倦访问字典，只需检查密钥是否在keys 中。您可以简单地这样做来实现相同的逻辑：

ex_dict = {'United States': '^GSPC','United States of America': '^GSPC', 'Usa': '^GSPC', 'Argentina': '^MERV'} #shortened on purpose

countries = []
print('Please choose five stock exchanges to analyse,' )
print('just name the corresponding countries \n')

for i in range(0, 5):
    while True:
        countr = input('Please enter country no. %d: ' %(i+1))
        countr = countr.title()
        if countr in ex_dict.keys():
            print('Found the corresponding stock index! \n')
            countries.append(countr)
            break
        else:
            print('Country not found, please try again! \n') 

示例运行：

Please choose five stock exchanges to analyse,
just name the corresponding countries 

Please enter country no. 1: sdf
Country not found, please try again! 

Please enter country no. 1: USA
Found the corresponding stock index! 

Please enter country no. 2: Aregtng
Country not found, please try again! 

Please enter country no. 2: Argentina
Found the corresponding stock index! 

Please enter country no. 3: United States
Found the corresponding stock index! 

Please enter country no. 4: usa
Found the corresponding stock index! 

Please enter country no. 5: usa
Found the corresponding stock index! 

注意：.keys() 太过分了：要检查一个键是否在字典中，你只需要k in some_dict

Answer 5

您的中断不在 if 范围内...所以它会在第一次尝试时中断。