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What is a generator function, and how does 'yield' make it different from a regular function? How do dict comprehensions and set comprehensions differ in syntax from list comprehensions? What is a generator expression, and how does it differ syntactically and behaviorally from a list comprehension? How do you write a nested comprehension, like flattening a list of lists into a single flat list? How does 'yield from' delegate iteration to a sub-generator, and what does it return as its own expression value? How does generator.throw() let you inject an exception into a paused generator, and how would the generator handle it? How does lazy evaluation in a chained sequence of generator expressions actually process elements, one at a time end-to-end, without intermediate lists? How would you implement a memory-efficient sliding window or batching generator over a large iterable? How do you correctly close a generator early and ensure any try/finally cleanup inside it still runs? How would you implement a coroutine-style generator-based pipeline (the classic pre-async/await pattern) using multiple chained 'send()'-driven generators?
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Python › Comprehensions & Generators

How do you send a value INTO a generator using the .send() method, and how does this differ from just calling next()?

Intermediate

Answer

generator.send(value) resumes the generator's execution and makes 'value' become the RESULT of the 'yield' expression that's currently paused — unlike next() (equivalent to send(None)), send() lets you communicate data back INTO the generator's ongoing execution, enabling coroutine-like two-way communication.
def echo():
    while True:
        received = yield
        print(f"Received: {received}")

gen = echo()
next(gen)          # prime the generator to the first yield
gen.send("hello")   # prints "Received: hello"
Real-world example Building a simple coroutine-style consumer that processes values pushed to it one at a time, a pattern predating async/await.

Common follow-ups: Why must you call next() (or send(None)) once to 'prime' a generator before you can send() a real value into it?

Functions & Scope
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