KITFORMA · EDITORIAL ANSWER
Why is a Python generator empty on the second pass?
KitForma editorial guide. A generator is a consumable iterator, not a replayable collection. Once exhausted, another loop has nothing left to retrieve.
Step-by-step answer
A generator is a consumable iterator, not a replayable collection. Once exhausted, another loop has nothing left to retrieve.
If repeated traversal is required and the result is bounded, materialize it once with
rows = list(generate_rows()). Otherwise expose a factory that creates a fresh generator for each pass. Test by consuming one element first and observing that the subsequent loop starts at the second element. Be careful with any, next and membership tests: they can consume an iterator too. Materializing an unbounded source is unsafe, and recreating a generator that performs I/O may repeat external side effects.Sources and verification
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