What does `itertools.chain(*iterables)` do and how is it more efficient than concatenation?

Question

Python Developer — Hard

What does `itertools.chain(*iterables)` do and how is it more efficient than concatenation?

Accepted Answer

`itertools.chain(*iterables)` returns an iterator that chains multiple iterables sequentially without creating an intermediate list in memory. This is more efficient than list concatenation, which builds a new list before iteration.