[issue18821] Add .lastitem attribute to takewhile instances
Raymond Hettinger added the comment: Oscar, the solution proposed by Serhiy looks like a better choice. I'm wary of increasing the API complexity of the itertools. Right now, their learnability is aided by having simple signatures and no side-values. The itertools are modeled on functional tools in other languages with mature APIs. I look to those languages to provide an indication of whether proposed features are needed in practice. AFAICT, there is no precedent for a takewhile-with-failed-value combo. I appreciate your request (especially because it was accompanied by a use case) but am going to decline. IMO, the module as a whole is better served by keeping the tools simple and clean. If an individual itertool doesn't have an exact fit to a particular use case, it may indicate that the programmer would be better served by a simple generator which can express the logic more cleanly than a tricked-out itertool with side-values. -- resolution: - rejected status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue18821 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue18821] Add .lastitem attribute to takewhile instances
Oscar Benjamin added the comment: Thank you Claudiu very much for writing a patch; I was expecting to have to do that myself! Serhiy, you're right groupby is a better fit for this. It does mean a bit of reworking for the (more complicated) sum function I'm working on but I've just checked with timeit and it performs very well using the type function as a predicate. I think it might make the function a few times faster than takewhile in my common cases for reasons that are particular to this problem. Raymond, thanks for taking the time to consider this. I agree that it should now be closed. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue18821 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue18821] Add .lastitem attribute to takewhile instances
Claudiu.Popa added the comment: Hello. Here's a basic patch with tests which accomplishes your request. Currently, it defaults to None if no item failed, but probably it can be set only when something fails the predicate (and the user will check using hasattr(t, 'last') ). -- keywords: +patch nosy: +Claudiu.Popa Added file: http://bugs.python.org/file31647/itertools_takewhile.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue18821 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue18821] Add .lastitem attribute to takewhile instances
Serhiy Storchaka added the comment: Oscar, did you considered itertools.groupby()? Perhaps it better meets your needs. -- nosy: +serhiy.storchaka ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue18821 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue18821] Add .lastitem attribute to takewhile instances
Changes by Raymond Hettinger raymond.hettin...@gmail.com: -- assignee: - rhettinger ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue18821 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue18821] Add .lastitem attribute to takewhile instances
New submission from Oscar Benjamin: I've often wanted to be able to query a takewhile object to discover the item that failed the predicate but the item is currently discarded. A usage example: def sum(items): it = iter(items) ints = takewhile(Integral.__instancecheck__, it) subtotal = sum(ints) if not hasattr(ints.lastitem): return subtotal floats = takewhile(float.__instancecheck__, it) subtotalf = fsum(floats) if not hasattr(floats.lastitem): return subtotal + subtotalf # Deal with more types ... Loosely what I'm thinking is this but perhaps with different attribute names: class takewhile(pred, iterable): def __init__(self): self.pred = pred self.iterable = iterable self.failed = False def __iter__(self): for item in self.iterable: if self.pred(item): yield item else: self.failed = True self.lastitem = item return -- components: Library (Lib) messages: 195962 nosy: oscarbenjamin priority: normal severity: normal status: open title: Add .lastitem attribute to takewhile instances type: enhancement versions: Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue18821 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue18821] Add .lastitem attribute to takewhile instances
Changes by Ned Deily n...@acm.org: -- nosy: +rhettinger ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue18821 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
