Python Python List Comprehensions and Generators 2

Question 1

What does `next()` do when called on a generator that is exhausted?

Accepted Answer

Raises a StopIteration exception

Answer

Once a generator has no more values to yield, calling next() raises StopIteration.

Question 2

What is the result of `[i*j for i in range(1,3) for j in range(1,3)]`?

Accepted Answer

[1, 2, 2, 4]

Answer

The nested comprehension iterates i over [1,2] and j over [1,2], producing 1*1=1, 1*2=2, 2*1=2, 2*2=4.

Question 3

Which built-in function can be used to create an iterator from any iterable?

Accepted Answer

iter()

Answer

iter() returns an iterator object from any iterable, calling its __iter__ method.

Question 4

What does `yield from` do in a generator function?

Accepted Answer

Delegates to a sub-generator, yielding all its values

Answer

yield from sub_gen delegates to a sub-generator, yielding each of its values as if they were in the outer generator.

Question 5

What is the output of `[x for x in [1,2,3,4,5] if x > 3]`?

Accepted Answer

[4, 5]

Answer

The filter condition x > 3 keeps only 4 and 5 from the original list.

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