您如何处理代码中的不同 KeyError

Question

Let say my dictionary can have 3 different key-value pairs. How do i handle different KeyError with if condition.

Let's say.

Dict1 = {'Key1': 'Value1, 'Key2': 'Value2', 'Key3': 'Value3' }

Now if I try Dict1['Key4'], it will through me KeyError: 'Key4',

I want to handle it

except KeyError as error:
     if str(error) == 'Key4':
        print (Dict1['Key3']
     elif str(error) == 'Key5':
        print (Dict1['Key2']
     else:
        print (error)

It's not getting captured in if condition, it still goes in else block.

Answer 1

Python KeyErrors are much longer than just the key used. You have to check if "Key4" is in the error, as opposed to checking if it is equal to the error:

except KeyError as error:
     if 'Key4' in str(error):
        print (Dict1['Key3'])
     elif 'Key5' in str(error):
        print (Dict1['Key2'])
     else:
        print (error)

Answer 2

You can also use a simple approach:

dict1 = {'Key1' : 'Value1', 'Key2': 'Value2', 'Key3': 'Value3' }

key4 = dict1['Key4'] if 'Key4' in dict1 else dict1['Key3']
key5 = dict1['Key5'] if 'Key5' in dict1 else dict1['Key2']

Answer 3

You could also just use dict.get() to give you a default value if the key doesn't exist:

dict1 = {'Key1' : 'Value1', 'Key2': 'Value2', 'Key3': 'Value3' }

print(dict1.get('Key4', dict1.get('Key3')))
# Value3

print(dict1.get('Key4', dict1.get('Key2')))
# Value2

From the docs :

Return the value for key if key is in the dictionary, else default. If default is not given, it defaults to None, so that this method never raises a KeyError