KeyError vs IndexError in Python Explained

KeyError and IndexError both happen when your code tries to access something that is not available.

The difference is simple:

KeyError is about a missing dictionary key
IndexError is about a list or tuple position that does not exist

If you can quickly tell whether you are working with a dictionary or a sequence like a list, you can usually fix the problem fast.

Quick fix

data = {"name": "Ana"}
items = [10, 20, 30]

# KeyError fix: check the key first or use get()
print(data.get("age"))  # None

# IndexError fix: check the index first
index = 5
if 0 <= index < len(items):
    print(items[index])
else:
    print("Index out of range")

Use dict.get() for possibly missing dictionary keys. Check the length before using a list or tuple index.

What is the difference between KeyError and IndexError?

KeyError happens when you ask a dictionary for a key that does not exist.
IndexError happens when you ask a list or tuple for a position that does not exist.
A key is a dictionary label like "name".
An index is a numeric position like 0, 1, 2.

For example:

user["email"] uses a key
items[2] uses an index

If you need a refresher, see Python dictionaries explained and Python lists explained.

When KeyError happens

KeyError is most common with dictionaries.

It happens when code like this tries to read a missing key:

user = {"name": "Ana"}
print(user["email"])

The dictionary exists, but "email" is not inside it.

Common causes:

Misspelled keys
Unexpected input data
Assuming JSON or API data always contains the same fields
Using the wrong object type

If you want a full guide, see KeyError in Python: causes and fixes.

When IndexError happens

IndexError is most common with lists and tuples.

It happens when code tries to access a position outside the valid range:

items = [10, 20, 30]
print(items[5])

The list exists, but index 5 is too large.

Common causes:

Loops that go too far
Hard-coded indexes
Empty lists
Assuming a list always has enough items

For a deeper explanation, see IndexError in Python: causes and fixes.

Example: KeyError

Here is a simple example that causes KeyError:

user = {"name": "Ana", "city": "Lima"}
print(user["email"])

Output:

KeyError: 'email'

Why it happens:

user is a dictionary
The code asks for the key "email"
That key is missing

Fix 1: Use `get()`

user = {"name": "Ana", "city": "Lima"}
print(user.get("email"))

Output:

None

get() returns None instead of raising an error if the key is missing.

You can also give a default value:

user = {"name": "Ana", "city": "Lima"}
print(user.get("email", "No email found"))

Output:

No email found

See Python dictionary get() method for more examples.

Fix 2: Check the key first

user = {"name": "Ana", "city": "Lima"}

if "email" in user:
    print(user["email"])
else:
    print("Key not found")

Fix 3: Add the missing key

user = {"name": "Ana", "city": "Lima"}
user["email"] = "ana@example.com"

print(user["email"])

Example: IndexError

Here is a simple example that causes IndexError:

items = [10, 20, 30]
print(items[5])

Output:

IndexError: list index out of range

Why it happens:

items is a list
Valid indexes are 0, 1, and 2
Index 5 does not exist

Fix 1: Check the index before using it

items = [10, 20, 30]
index = 5

if 0 <= index < len(items):
    print(items[index])
else:
    print("Index out of range")

Fix 2: Change loop logic

Bad example:

items = [10, 20, 30]

for i in range(5):
    print(items[i])

This fails because the loop tries indexes that do not exist.

Better:

items = [10, 20, 30]

for i in range(len(items)):
    print(items[i])

Best for beginners:

items = [10, 20, 30]

for item in items:
    print(item)

Looping directly over the list avoids many index mistakes.

If needed, review the len() function explained.

How to choose the right fix

When you see the error, first look at the object you are accessing.

If the code uses square brackets on a dictionary, check the key
If the code uses square brackets on a list or tuple, check the position
Print the object to confirm what it contains
Use type() if you are not sure what kind of object you have

Example:

data = {"name": "Ana"}
items = [10, 20, 30]

print(type(data))
print(type(items))

Output:

<class 'dict'>
<class 'list'>

A good rule:

Dictionary + missing label = KeyError
List or tuple + bad numeric position = IndexError

Beginner debugging steps

If you are not sure what is wrong, use these steps:

Read the last line of the traceback first
Find the variable being accessed
Check whether it is a dictionary, list, or tuple
Inspect the available keys or valid indexes
Check for empty data structures

Useful debugging commands:

print(type(data))
print(data)
print(data.keys())

print(len(items))
print(index)
print(list(enumerate(items)))

What these help you see:

print(type(data)) shows the object type
print(data) shows the current contents
print(data.keys()) shows dictionary keys
print(len(items)) shows how many items are in the list
print(index) shows the index you are trying to use
print(list(enumerate(items))) shows each item with its index

Common causes beginners mix up

These mistakes often cause confusion:

Treating a dictionary like a list
Treating a list like a dictionary
Assuming API or JSON data always contains the same keys
Assuming a list always has enough items

Other common causes:

Using data["missing_key"] on a dictionary
Misspelling a dictionary key
Expecting JSON data to contain a key that is not present
Using list[index] with an index larger than len(list) - 1
Accessing index 0 on an empty list
Using the wrong data type for the operation

Quick comparison table

Error	Usually happens with	What is missing	Example	Common fix
`KeyError`	Dictionary	Key	`user["email"]`	Use `get()` or check `if key in dict`
`IndexError`	List or tuple	Valid position	`items[5]`	Check bounds with `len()`

Another quick way to remember it:

KeyError uses labels like "name"
IndexError uses positions like 0 or 3

FAQ

Is KeyError only for dictionaries?

Mostly yes for beginner use. It usually appears when a dictionary key is missing.

Does IndexError happen with dictionaries?

No. IndexError is for sequences like lists and tuples, not dictionary keys.

Should I use get() to avoid KeyError?

Yes, if a missing key is acceptable. get() returns a default value instead of raising KeyError.

If you want examples, see how to check if a key exists in a dictionary in Python.

How do I avoid IndexError in a loop?

Loop directly over the list when possible, or make sure the index stays below len(list).