The error message:
TypeError: 'NoneType' object is not subscriptable
occurs when you try to index ([]) or slice ([:]) a None value, which is not allowed in Python.
1. Causes and Solutions
Cause 1: A Function Returns None Instead of a List or String
If a function returns None, trying to access elements using [] will cause this error.
Incorrect Code:
def get_list():
print("Returning list") # No return statement, so it returns None
result = get_list()
print(result[0]) # TypeError: 'NoneType' object is not subscriptable
Solution: Return a Proper List or String
def get_list():
return ["apple", "banana", "cherry"] # Proper return value
result = get_list()
print(result[0]) # Output: apple
Cause 2: Variable Assigned None Instead of a List or String
If you accidentally assign None instead of a list or string, you cannot use indexing.
Incorrect Code:
data = None
print(data[0]) # TypeError
Solution: Ensure the Variable is a List or String
data = "Python"
print(data[0]) # Output: P
Cause 3: Forgetting to Return a Value in a Function
If a function doesn’t explicitly return a value, it returns None by default.
Incorrect Code:
def find_element():
numbers = [10, 20, 30]
numbers.index(40) # No return value if 40 is not found
result = find_element()
print(result[0]) # TypeError
Solution: Return a Proper Value
def find_element():
numbers = [10, 20, 30]
return numbers.index(20) # Return an actual index
result = find_element()
print(result) # Output: 1
Cause 4: Calling .get() on a Dictionary Without a Default Value
Using .get() on a dictionary returns None if the key is missing.
Incorrect Code:
data = {"name": "Alice"}
print(data.get("age")[0]) # TypeError: 'NoneType' object is not subscriptable
Solution: Provide a Default Value
print(data.get("age", "Unknown")[0]) # Output: U
2. Best Practices to Avoid TypeError
Check if a function returns None before using indexing
Ensure variables hold valid iterables (list, tuple, or string)
Use if result is not None: to verify before indexing
Use .get(key, default_value) when accessing dictionary values