On Dec 5, 2019, at 08:53, Juancarlo Añez <apalala@gmail.com> wrote:

BTW, a common function in extensions to itertools is first():

def first(seq, default=None):
return next(iter(seq), default= default)

That function, first(), would also be a nice addition in itertools, and findfirst() could be implemented using it. first() avoids most use cases needing to check if a sequence or iterator is empty before using a default value. MHO is that first() deals with so many common cases that it should be a builtin.

I think this was proposed for itertools and rejected. I don’t remember why, but generally there’s resistance to adding anything that you could write yourself (and are unlikely to get wrong) on top of itertools and builtins, unless it needs to loop and yield itself (in which case it might need the performance boost of iterating in C instead of Python), because that’s what the recipes are for. And I suppose if you see the recipe for nth you don’t learn anything from the recipe for first.

But people seem more open to recipes being “everything useful” rather than only “everything useful that also teaches an important idea”, and the recipe docs even link to more-itertools for people looking to use them out of the box (and first is in more-itertools). Also, I think it’s pretty clear that people often don’t think of first when they need it, so even if they could write it if they thought of it, they don’t because they don’t.

So maybe it’s worth at least adding first as a recipe, even if people don’t think it’s worth adding to the module itself?

(Personally, I use first if I’ve already imported more-itertools for something else, but otherwise I just next Iter.)