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How do you write a basic list comprehension, and how does it compare to an equivalent for loop? How do you add a filtering condition to a list comprehension using 'if'? 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 '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?
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Python › Comprehensions & Generators

What is a generator function, and how does 'yield' make it different from a regular function?

Beginner

Answer

A generator function contains at least one 'yield' statement; calling it doesn't run the function body immediately — it returns a generator object, and the body only executes incrementally, one step at a time, each time you request the next value (via next() or a for loop).
def count_up_to(n):
    i = 1
    while i <= n:
        yield i
        i += 1

for number in count_up_to(3):
    print(number)  # 1, 2, 3
Real-world example Lazily producing a sequence of values one at a time instead of building and returning a full list upfront.

Common follow-ups: What exception is raised internally when a generator is exhausted and next() is called again?

Iterators & the Iterator Protocol
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