chain.from_iterable

Question

chain.from_iterable

Accepted Answer

chain.from_iterable() accepts a single iterable of iterables and flattens one level deep - it's equivalent to chain(*groups) but avoids unpacking the whole list into positional arguments at once. This matters when groups is a lazy generator itself: chain(*generator) would exhaust it to build the argument list, whereas chain.from_iterable(generator) stays lazy. Use from_iterable any time your source is itself a generator or you're flattening a list of unknown length.