Python 当键不在字典中时，如何使用异常处理创建for循环？_Python_For Loop_Dictionary_Exception

Python 当键不在字典中时，如何使用异常处理创建for循环？

python for-loop dictionary exception

Python 当键不在字典中时，如何使用异常处理创建for循环？,python,for-loop,dictionary,exception,Python,For Loop,Dictionary,Exception,所以，我有一本字典，上面有国家名称和相应的股票指数。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我被要求输入时，我对照字典检查是否能找到国家，这种情况发生了五次。现在，处理异常的部分并不是我所希望的。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'} #shor

所以，我有一本字典，上面有国家名称和相应的股票指数。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

当我被要求输入时，我对照字典检查是否能找到国家，这种情况发生了五次。现在，处理异常的部分并不是我所希望的。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')

您的中断不在if范围内。。。因此，它将在第一次尝试时中断。

此处不会出现

键错误

，因为您的代码访问字典时不会感到厌倦，只需检查键是否在

键中。您可以简单地执行此操作以实现相同的逻辑：
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') 

样本运行：
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，您只需要在某些目录中使用k这里就不会出现KeyError
，因为您的代码永远不会厌倦访问字典，只需检查键是否在keys
中即可。您可以简单地执行此操作以实现相同的逻辑：
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') 

样本运行：
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：要检查某个键是否在字典中，您只需要从
每当请求dict（）对象（使用格式a=adict[key]），并且该键不在字典中时，Python都会引发一个KeyError
在您的代码段中，如果您希望在用户插入countries dict中不存在的密钥时打印消息，您可以简单地添加else语句，而不是catch exception
您可以通过以下方式更改代码：
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')

从
每当请求dict（）对象（使用格式a=adict[key]），并且该键不在字典中时，Python都会引发一个KeyError
在您的代码段中，如果您希望在用户插入countries dict中不存在的密钥时打印消息，您可以简单地添加else语句，而不是catch exception
您可以通过以下方式更改代码：
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')

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（）
而且，有很多循环。我认为对于在（0,5）范围内的I来说就足够了。将变得不那么复杂
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>

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（）
而且，有很多循环。我认为对于在（0,5）范围内的I来说就足够了。将变得不那么复杂
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>

我假设你想让它给你一个消息，如果股票不在字典里，我修改了代码做同样的事情
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)

我假设你想让它给你一个消息，如果股票不在字典里，我修改了代码做同样的事情
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)

你希望它能做什么，它能做什么呢？你不需要捕捉关键错误，因为你不会遇到关键错误。也可以使用if countr in ex_dict
而不是if countr in ex_dict.keys（）
一个简单的else语句而不是捕获KeyError来解决您的问题您希望它做什么，它做什么呢？您不需要捕获KeyError，因为您不会遇到这样的错误。也可以使用if countr in ex_dict
而不是if countr in ex_dict.keys（）
一个简单的else语句而不是捕获KeyError来解决您的问题。您是否尝试了该代码？它在有错误和无错误的情况下都能很好地循环。我的意思是，一个带中断的while循环保证会触发是没有意义的。但我承认这并没有回答你关于捕获异常的问题。。。正如其他人所说，在ex_dict.keys（）中尝试countr时，代码没有引发任何键错误。
您是否尝试了该代码？它在有错误和无错误的情况下都能很好地循环。我的意思是，一个带中断的while循环保证会触发是没有意义的。但我承认这并没有回答你关于捕获异常的问题。。。正如其他人所说，在ex_dict.keys（）中尝试countr时，代码没有引发任何键错误。