What is a StopIteration?

StopIteration is raised by an iterator's __next__() method to signal that there are no more items to produce. It is the normal termination signal for iterators and is automatically caught by for loops, but it will propagate as an error if you call next() manually without a default.

Why it happens

• •Calling next() on an iterator that has already been fully consumed.
• •Using next() inside a generator function, which causes the generator itself to stop.
• •Manually iterating with next() instead of using a for loop, without providing a default value.
• •Consuming a generator or iterator in one place and then trying to iterate it again (iterators cannot be rewound).

Examples

numbers = iter([1, 2, 3])

print(next(numbers))  # 1
print(next(numbers))  # 2
print(next(numbers))  # 3
print(next(numbers))  # iterator is exhausted

1
2
3
Traceback (most recent call last):
  File "app.py", line 6, in <module>
    print(next(numbers))
StopIteration

numbers = iter([1, 2, 3])

# Use a default value to avoid the exception
value = next(numbers, None)
while value is not None:
    print(value)
    value = next(numbers, None)

# Or simply iterate with a for loop:
for n in [1, 2, 3]:
    print(n)

Related errors

• ValueError
• IndexError