TFA explains this, although they never actually links the StackOverflow answer that they quote from. > CPython’s list.sort is implemented in C (avoiding interp

TFA explains this, although they never actually links the StackOverflow answer that they quote from. > CPython’s list.sort is implemented in C (avoiding interpreter overhead), while heapq.merge is mostly implemented in Python, and optimizes for the “many iterables” case in a way that slows the “two iterables” case. Going to the original StackOverflow answer, we can see the same user (ShadowRanger) expanding on this in a comment: https://stackoverflow.com/questions/464342/combining-two-sorted-lists-in-python https://stackoverflow.com/questions/464342/combining-two-sor... > The selling point for heapq.merge is that it doesn't require either the inputs or the outputs to be list; it can consume iterators/generators and produces a generator, so huge inputs/outputs (not stored in RAM at once) can be combined without swap thrashing. It also handles merging an arbitrary number of input iterables with lower overhead than might be expected (it uses a heap to coordinate the merging, so the overhead scales with the log of the number of iterables, not linearly, but as noted, that doesn't matter for the "two iterable" case).