In Python, KeyError occurred when try access a value in dictionary by key name but key don’t exist. If key found in dictionary will return a value if doesn’t exist then through KeyError : key_name .

How to handle KeyError in Python?

You can handle KeyError while accessing the key from dictionary by following ways:

• Check for key in advance for accessing the key
• Use the ‘in’ keyword to check for key
• Use try and except block.

Example of KeyError in Python

Lets take simple example where user want to access key from dictionary to retrieve value. In this example if user input key name, age or city either of them then it will return value. if user input other value as key that doesn’t exist in dictionary then it will throw exception as KeyError: passing_key.

user = {
    "name": "Saurabh Gupta",
    "age": 35,
    "city": "Noida"
}

key_name=input("What information you want to get? (name, age, city)")
print(key_name+" :"+user[key_name])

Now as suggested above solution to KeyError, lets fix the above to problem to exception handle and show message in case user input other keys except in dictionary.

Solution 1 : Iterate all key and value

Lets take first solution to get keys from dictionary then retrieve values from dictionary.

user = {
    "name": "Saurabh Gupta",
    "age": 35,
    "city": "Noida"
}
#iterate user dictionary
for key, value in user.items():
    print("Key:", key)
    print("Value:", str(value))

In this solution user will able to print all values w.r.t each key.

Solution 2 : Advance check by in

Lets take second solution to fix this problem to check key in dictionary first by using ‘in’ in if statement. if key not available in dictionary then print else statement.

user = {
    "name": "Saurabh Gupta",
    "age": 35,
    "city": "Noida"
}

key_name=input("What information you want to get? (name, age, city)")
if key_name in user:
    print(key_name+" :"+user[key_name])
else:
    print(key_name +" key is not available in user")

in this solution if user input any key like name, age or city then print value otherwise print as key is not available.

Solution 3 : try and except

Lets take third solution to solve KeyError by using exception handling through try and except.

user = {
    "name": "Saurabh Gupta",
    "age": 35,
    "city": "Noida"
}

key_name=input("What information you want to get? (name, age, city)")
try:
    print(key_name+" :"+user[key_name])
except KeyError:
    print(key_name +" key is not available in user")

In this solution if key is correct then print value w.r.t key in dictionary. if key doesn’t exist and KeyError exception occurs the print statement as “Key is not available in user”.

To learn more on exception handling follow the link Python: Exception Handling.

If this blog for solving KeyError help you to resolve problem make comment or if you know other way to handle this problem write in comment so that it will help others.