RuntimeError: Generator Raised StopIteration

Why This Happens

In Python 3.7+, StopIteration propagating out of a generator is converted to RuntimeError to prevent silent bugs. Use return to end a generator, not raise StopIteration.

The Problem

def my_gen(items):
    it = iter(items)
    while True:
        yield next(it)  # StopIteration escapes!

The Fix

def my_gen(items):
    it = iter(items)
    while True:
        try:
            yield next(it)
        except StopIteration:
            return  # Use return to end generator

Step-by-Step Fix

1. 1

   Use return instead

   End generators with return, not raise StopIteration.

2. 2

   Catch StopIteration

   Wrap next() calls in try/except inside generators.

3. 3

   Use yield from

   Use 'yield from iterable' to delegate to another iterator.