Nick, sorry, but your arguments still make little sense to me. I think you're pushing an analogy between `sum()` details and `accumulate()` waaaaay too far, changing a simple idea into a needlessly complicated one.
`accumulate()` can do anything at all it wants to do with a `start` argument (if it grows one), and a "default" of start=0 makes no sense: unlike `sum()`, `accumulate()` is not specifically for use with numeric values and may reject non-numeric types [from the `sum()` docs] `accumulate()` accepts any two-argument function. >>> itertools.accumulate([1, 2, 3], lambda x, y: str(x) + str(y)) <itertools.accumulate object at 0x0000028AB1B3B448> >>> list(_) [1, '12', '123'] Arguing that it "has to do" something exactly the way `sum()` happens to be implemented just doesn't follow - not even if they happen to give the same name to an optional argument. If the function were named `accumulate_sum()`, and restricted to numeric types, maybe - but it's not. [Nick Coghlan <ncogh...@gmail.com>] > ... > That concern mostly goes away if the new parameter is deliberately > called something *other than* "start" (e.g. "prepend=value", or > "first=value"), but it could also be addressed by offering a dedicated > "yield_start" toggle, such that the revised semantics were: > > def accumulate(iterable, func=operator.add, start=0, > yield_start=False): > it = iter(iterable) > total = start > if yield_start: > yield total > for element in it: > total = func(total, element) > yield total > > That approach would have the advantage of making the default value of > "start" much easier to document (since it would just be zero, the same > as it is for sum()), and only the length of the input iterable and > "yield_start" would affect how many partial sums were produced. As above, start=0 is senseless for `accumulate` (despite that it makes sense for `sum`). Raymond gave the obvious implementation in his original message. If you reworked your implementation to accommodate that NO sensible default for `start` exists except for the one Raymond used (a unique object private to the implementation, so he knows for sure whether or not `start` was passed), you'd end up with his implementation ;-) `yield_start` looks like a nuisance in any case. As already explained, most uses want the `start` value if it's given, and in cases where it isn't it's trivial to discard by doing `next()` once on the result. Of course it could be added - but why bother? _______________________________________________ Python-ideas mailing list Pythonemail@example.com https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/