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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'? What is a generator function, and how does 'yield' make it different from a regular function? 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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How do dict comprehensions and set comprehensions differ in syntax from list comprehensions?

Intermediate

Answer

A dict comprehension uses curly braces with a 'key: value' pair (`{k: v for ...}`), producing a dictionary; a set comprehension uses curly braces with just an expression (`{expr for ...}`, no colon), producing a set with automatically deduplicated values — both otherwise support the same for/if clauses as list comprehensions.
squares_dict = {n: n * n for n in range(5)}
print(squares_dict)  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

unique_lengths = {len(word) for word in ["cat", "dog", "bird", "ox"]}
print(unique_lengths)  # {3, 4, 2}
Real-world example Building a lookup dictionary from a list of objects (keyed by ID), or a set of unique values derived from a list.

Common follow-ups: How would you write a comprehension that produces a dict from two PARALLEL lists using zip()?

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All 15 Comprehensions & Generators questions