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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 do you send a value INTO a generator using the .send() method, and how does this differ from just calling next()? 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? How do you write a comprehension with MULTIPLE 'if' conditions, and how does that differ from combining them with 'and'?
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How does 'yield from' delegate iteration to a sub-generator, and what does it return as its own expression value?

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Answer

'yield from sub_generator' fully delegates yielding to the sub-generator, forwarding each of its values as if they were yielded directly by the outer generator — AND its expression evaluates to whatever the sub-generator eventually returns (via a 'return' statement), letting you compose generators while still capturing a final result.
def inner():
    yield 1
    yield 2
    return "inner done"

def outer():
    result = yield from inner()
    print(result)  # "inner done", printed after inner's values are yielded
    yield 3

list(outer())  # yields 1, 2, 3; prints "inner done" in between
Real-world example Composing a large generator out of smaller, reusable generator building blocks, similar to function composition.

Common follow-ups: How does 'yield from' also automatically forward .send() and .throw() calls into the delegated sub-generator?

Iterators & the Iterator Protocol
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