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ERROR KeyError
Python KeyError
Python Error
A dictionary key does not exist.
Root Cause
Accessing a dictionary with a key that has not been set, or the key was deleted.
How to Fix
Use dict.get(key, default) to safely access keys. Check if the key exists with 'key' in dict before accessing. Use defaultdict for automatic default values.
Quick Summary
KeyError means you accessed a dictionary key that does not exist. Use dict.get(key, default) for safe access, or check with 'key' in dict before accessing.
Key Takeaways
Key Takeaways
- dict[key] raises KeyError if key does not exist
- dict.get(key, default) returns default instead of raising
- Check existence: if 'key' in dict:
- Use collections.defaultdict for automatic default values
Use Cases
When to use it
- Accessing a missing key in a JSON response
- Dictionary key was deleted or never set
- Typo in the key name
Watch out
Common Mistakes
- Using dict[key] instead of dict.get(key) when the key might not exist
- Not handling KeyError in code that processes external data
FAQ
KeyError Python KeyError, Frequently Asked
What is the difference between dict[key] and dict.get(key)?
dict[key] raises KeyError if the key is missing. dict.get(key) returns None (or a specified default) without raising.
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