How does a generator help process a large file without loading it all into memory?

A generator yields values lazily and retains enough state to resume on the next iteration. Iterating over an open text file and yielding matching lines avoids building a list of every line. Memory still depends on individual line sizes and downstream consumers; converting the generator to a list removes the streaming advantage. Use a context manager so the file closes reliably. This generator keeps the file open while it is being consumed, so callers should finish iteration or close it when stopping early.