ProjectStack

python

StopIteration

StopIteration signals that an iterator has no more items to produce. Calling next() on an exhausted iterator raises this. Inside a generator, it's normal, but leaking outside a generator function can crash your code in Python 3.7+.

Common causes

Calling next() on an iterator that has already been fully consumed
Using next() without a default value on an empty iterator: next(iter([]))
A StopIteration raised inside a generator function is converted to a RuntimeError in Python 3.7+
Manually iterating a file or database cursor past the last record

How to fix it

Use next() with a default to avoid the exception: next(iterator, None)
Use a for loop instead of next() — it handles StopIteration automatically
Check if the iterable is empty before calling next(): if items: next(iter(items))
In generators, use return instead of raising StopIteration

Example

Traceback (most recent call last):
  File "app.py", line 4, in <module>
    first = next(empty_iterator)
StopIteration

Calling next() on an iterator built from an empty list

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