When working with Python, you might encounter a variety of errors and exceptions. This tutorial aims to guide you through resolving one of the common errors in Python, a KeyError
Understanding KeyError in Python
A KeyError usually occurs when you try to access a dictionary key that doesn’t exist. Dictionary keys in Python should always be unique, and attempting to access a key that is not present in the dictionary triggers a KeyError.
Example of KeyError
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info = {'name': 'Python', 'version': 3.7} print(info['year']) |
The above code will raise a KeyError because ‘year’ is not a key in the dictionary info.
Step 1: Check if the KeyError really exists
Make sure the key you’re trying to access is in the dictionary. You can use the in
keyword to check if the key exists or not:
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if 'year' in info: print(info['year']) |
Step 2: Use get() function to avoid KeyError
In Python, dictionaries have a built-in method called get(). This method returns the value for the given key if it exists. Otherwise, it returns a default value that you can specify.
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print(info.get('year', 'Key does not exist')) |
Step 3: Use dict.setdefault method
This method returns the value of a key (if the key is in a dictionary). If not, it inserts a key with a value to the dictionary.
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print(info.setdefault('year', 'Key does not exist')) |
Full Code
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info = {'name': 'Python', 'version': 3.7} # Check if key exists if 'year' in info: print(info['year']) # Use get() function print(info.get('year', 'Key does not exist')) # Use set default method print(info.setdefault('year', 'Key does not exist')) |
Conclusion
In this tutorial, we have discussed how to solve a KeyError in Python. We have explored some built-in dictionary methods to prevent this exception from occurring.
Remember, when dealing with data structures in Python, being aware of the specific functions and methods at your disposal can aid in writing clean, error-free code.