When does the
IndexError: list assignment index out of range appear?
Python throws an
IndexError if you try to assign a value to a list index that doesn’t exist, yet. For example, if you execute the expression
list = 10 on an empty
list, Python throws the
IndexError. Simply resolve it by adding elements to your list until the index actually exists.
Here’s the minimal example that throws the IndexError:
lst =  lst = 10
If you run this code, you’ll see that Python throws an
Traceback (most recent call last): File "C:\Users\xcent\Desktop\code.py", line 2, in <module> lst = 10 IndexError: list assignment index out of range
You can resolve it by adding two “dummy” elements to the list so that the index 1 actually exists in the list:
lst = [None, None] lst = 10 print(lst)
Now, Python will print the expected output:
Try to fix the
IndexError in the following interactive code shell:
Exercise: Can you fix this code?
So what are some other occurrences of the IndexError?
IndexError in For Loop
IndexError happens if you use a
for loop to modify some list elements like here:
# WRONG CODE: lst =  for i in range(10): lst[i] = i print(lst)
Again, the result is an
Traceback (most recent call last): File "C:\Users\xcent\Desktop\code.py", line 4, in <module> lst[i] = i IndexError: list assignment index out of range
You modify a list element at index
i that doesn’t exist in the list. Instead, create the list using the
list(range(10)) list constructor.
# CORRECT CODE: lst = list(range(10)) print(lst) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
Where to Go From Here?
You’ve learned how to resolve one error. By doing this, your Python skills have improved a little bit. Do this every day and soon, you’ll be a skilled master coder.
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While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
To help students reach higher levels of Python success, he founded the programming education website Finxter.com. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.