Quick Answer

Handle missing dictionary keys.

Understanding the Issue

KeyError occurs when accessing non-existent dictionary keys.

The Problem

This code demonstrates the issue:

Python Error 
data = {"a": 1}
print(data["b"])

The Solution

Here's the corrected code:

Python Fixed 
# Use get() with default:
value = data.get("b", 0)

# Check first:
if "b" in data:
    value = data["b"]

# try/except:
try:
    value = data["b"]
except KeyError:
    value = None

Key Takeaways

Always handle missing keys safely.