KeyError Exception in Python

A KeyError exception is raised when you are trying to access an invalid key in a python dictionary. It tells you that there was an issue retrieving the key you were trying to access. It is part of the LookupError Exception class.

Example 1

Code

pylenin_info = {'name': 'Lenin Mishra',
                'age': 28,
                'language': 'Python'}
user_input = input('What do you want to learn about Pylenin==> ')

if user_input:
    print(f'{user_input} is {pylenin_info[user_input]}')
else:
    print(f'{user_input} is unknown')

The above code uses input() function and f-strings. Check them out.

Output

What do you want to learn about Pylenin==> wife
Traceback (most recent call last):
  File "some_file_location", line 7, in <module>
    print(f'{user_input} is {pylenin_info[user_input]}')
KeyError: 'wife'

As you can see, when you are trying to access an unavailable key, Python throws you a KeyError. You can handle this error using the KeyError Exception class in Python.

Example 2 - Handling KeyError in Python

Code

pylenin_info = {'name': 'Lenin Mishra',
                'age': 28,
                'language': 'Python'}
user_input = input('What do you want to learn about Pylenin==> ')

try:
    print(f'{user_input} is {pylenin_info[user_input]}')
except KeyError as e:
    print(f'{e}, {e.__class__}')

Output

What do you want to learn about Pylenin==> wife
'wife', <class 'KeyError'>

Check out other Python Built-in Exception classes in Python.

built-in-exception-classes - Pylenin

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