Python KeyError Exception Handling Examples

1. What is Python KeyError Exception?

Python KeyError is raised when we try to access a key from dict, which doesn’t exist. It’s one of the built-in exception classes and raised by many modules that work with dict or objects having key-value pairs.

2. Python KeyError with Dictionary

Let’s look at a simple example where KeyError is raised by the program.

emp_dict = {'Name': 'Pankaj', 'ID': 1}

emp_id = emp_dict['ID']
print(emp_id)

emp_role = emp_dict['Role']
print(emp_role)

Output:

1
Traceback (most recent call last):
  File "/Users/pankaj/Documents/PycharmProjects/hello-world/journaldev/errors/keyerror_examples.py", line 6, in <module>
    emp_role = emp_dict['Role']
KeyError: 'Role'

3. Python KeyError Exception Handling

We can handle the KeyError exception using the try-except block. Let’s handle the above KeyError exception.

emp_dict = {'Name': 'Pankaj', 'ID': 1}

try:
    emp_id = emp_dict['ID']
    print(emp_id)

    emp_role = emp_dict['Role']
    print(emp_role)
except KeyError as ke:
    print('Key Not Found in Employee Dictionary:', ke)

Output:

1
Key Not Found in Employee Dictionary: 'Role'

4. Avoiding KeyError when accessing Dictionary Key

We can avoid KeyError by using get() function to access the key value. If the key is missing, None is returned. We can also specify a default value to return when the key is missing.

emp_dict = {'Name': 'Pankaj', 'ID': 1}

emp_id = emp_dict.get('ID')
emp_role = emp_dict.get('Role')
emp_salary = emp_dict.get('Salary', 0)

print(f'Employee[ID:{emp_id}, Role:{emp_role}, Salary:{emp_salary}]')

Output: Employee[ID:1, Role:None, Salary:0]

5. KeyError Raised by Pandas Module

There are a few functions in Pandas DataFrame that raises KeyError exception.

• rename()
• drop()

6. References

• Python Exception Handling – Python try except
• KeyError Wiki Page