Stephen, dropwhile(None, ...) was an example, takewhile(None, ...) doesn't works either and it makes a lot of sense IMO.
On Thu, Nov 3, 2016 at 7:07 AM, Stephen J. Turnbull < turnbull.stephen...@u.tsukuba.ac.jp> wrote: > Francisco Couzo writes: > > > I'd be interested in writing a patch to make itertools more consistent > if > > there's a consensus. > > I don't understand what you mean by "consistent". I would argue that > in Python, an argument of None means "use the TOOWTDI default". For > "filterfalse", bool() is pretty obvious for the default predicate > since most Python classes do have a boolean interpretation. For > "groupby", I guess the identity is the "intuitive" default. But for > dropwhile, bool() or the identity seem like obvious choices, but > intuitively they're not very useful since the head of what's left is a > false-y. When would you want that? Typically false-ies are "nothing > to see here, people, move along" values. I guess that consideration > suggest lambda x: not(x), but I don't see why one would want to spell > that dropwhile(None, ...) rather than dropwhile(not, ...), especially > since in many contexts what you might really want (and expect None to > default to) is dropwhile(lambda x: x is None, ...). > > Bottom line for me is that this use (and non-use) of None is consistent > with Python practice regarding defaults. > > So, "accepts None" vs "doesn't accept None" doesn't seem to me to be > an important enough consistency to impose unobvious semantics on > dropwhile(None, ...). > >
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