How to Fix: StopIteration Error in Python

This “error” is actually a normal part of Python’s machinery, and in this case refers to the StopIteration Error. It’s not a bug; it’s a signal.

StopIteration is the exception that gets raised when an iterator (like a generator or file object) has no more items to give.

The Cause

You almost never see this in a for loop, because the for loop is designed to automatically catch this signal and stop.

You only see StopIteration when you are manually using the next() function.

Problem Code:

my_list = [1, 2]
my_iterator = iter(my_list) # Get an iterator for the list

print(next(my_iterator)) # Output: 1
print(next(my_iterator)) # Output: 2
print(next(my_iterator)) # CRASH! StopIteration

The program crashes because you asked for a third item, but the list was empty.

The Fix: Use try/except (If you must use next())

If you’re manually calling next(), you must also manually catch the StopIteration.

my_list = [1, 2]
my_iterator = iter(my_list)

try:
    while True:
        item = next(my_iterator)
        print(item)
except StopIteration:
    print("All items have been processed.")

The Real Fix: Use a for loop

The for loop does all of this for you. It’s cleaner, safer, and what you should use 99% of the time.

# This is the correct, Pythonic way
my_list = [1, 2]
for item in my_list:
    print(item)