Python KeyError Explained: Why It Happens and How to Fix It

Originally published on CodingCush. A Python KeyError means your code asked a dictionary for a key that does not exist in that dictionary. Python cannot guess what you wanted, so it stops the program and shows the missing key by name. It is one of the most common errors beginners meet, and the good news is that it is also one of the easiest to understand and fix once you know why it happens. What a KeyError Looks Like Here is the smallest example that causes the error. We create a dictionary for a student, then ask for a key that was never added. student = {"name": "Priya", "age": 21} print(student["city"]) Python replies with a short message like this: Traceback (most recent call last): File "main.py", line 3, in <module> print(student["city"]) KeyError: 'city' Read that last line carefully. Python is telling you the exact key it could not find, in this case city. The traceback also shows the file name and line number, so you know where to l