This guide explains keyerror and indexerror: handling missing data through a focused Python example. You will learn the behavior to expect, why it matters in a real program, and how to recognize the common mistakes before applying it in your own project.
What You Will Learn
KeyError reports a missing dictionary key, while IndexError reports a sequence position outside its valid range. Use get when missing keys are normal and length checks when indexing is optional.
When and Why to Use It
The following example focuses on a practical use of KeyError and IndexError: Handling Missing Data.
Step-by-Step Example
record = {"name": "Ari"}
items = ["first"]
print(record.get("email", "not provided"))
try:
print(items[3])
except IndexError:
print("No item at that position")Understanding the Example
Missing email uses a deliberate default, while the list access is handled as an invalid index. The two collection types signal different missing-data problems.
Expected Output
not provided
No item at that positionImportant Behavior and Edge Cases
A missing key is not the same as a key whose value is None. Decide which state you intend to represent.
Try It Yourself
Read an optional city from a dictionary and safely select an optional list element.
Common Beginner Mistakes
- A missing key is not the same as a key whose value is None. Decide which state you intend to represent.
- Handling the symptom rather than identifying the failing operation, or letting a broad exception handler hide defects.
- Skipping the practice step and assuming the example covers every input. Test at least one normal case and one edge case relevant to this topic.
Key Takeaways
- KeyError reports a missing dictionary key, while IndexError reports a sequence position outside its valid range.
- Missing email uses a deliberate default, while the list access is handled as an invalid index.
- Apply the technique deliberately, checking its documented input requirements and failure behavior before integrating it into a larger project.