What are generators in Python and how do they work?

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A generator is a function that yields values one at a time instead of returning them all at once. It pauses execution at each yield and resumes from where it left off when the next value is requested. How it works under the hood: the interpreter compiles def s that contain yield into generator-function objects. Each generator object holds its own stack frame, locals, and instruction pointer. yield suspends the frame and returns a value to the caller; next() restores the frame and continues. When the function returns (or falls off the end), the generator raises StopIteration , which is what ends a for loop. Generator expressions — a one-liner form, nearly identical to a list comprehension but with parentheses: The file processing example (constant memory for huge files) is the strongest practical argument. Show the generator pipeline pattern (composable, lazy processing). Know the difference between yield (pause) and return (terminate). Generator expressions vs list comprehensions for memory efficiency.