[issue22101] collections.abc.Set doesn't provide copy() method
Akira Li added the comment: I don't think this is needed nor do I think that it is a good idea to have a copy() method in the ABCs because they know so little about their concrete underlying class (perhaps the backing store in the filesystem or a database). Besides, a user already has workable alternatives such as creating a new instance and applying |= to populate it. because they know so little about their concrete underlying class FYI, the patch demonstrates how to implement copy() for *any* MutableSet: def copy(self): return self._from_iterable(self) _from_iterable() default implementation is cls(self) i.e., the copy() method may be also efficient by default e.g., it may return the object itself for immutable types. --- The issue is closed so the rest can be ignored. In general, we don't do API expansions without motivating use cases to guide the design. The reason to add Set.copy() is the same one as for set.copy() i.e., add the equivalent of L[:] to mutable containers that don't support slicing as the documentation excerpt in msg224255 explicitly says (copy() doesn't modify its object so it can be added to immutable type). General purpose language should provide an ability to copy a container. In practice, people spell this operation as CustomSet(s) thus hardcoding the type and ruining the flexibility provided by s.copy() duck-typing (or copy.copy()). The same could be said about MutableMapping (separate issue) e.g., merge a, b dictionaries assuming no .copy() method: d = dict(a) d.update(b) vs. the same with .copy(): d = a.copy() d.update(b) The latter may also work for a custom dict. The former is hardcoded to produce a dict e.g., you have to reimplement it (and all the surrounding code) for OrderedDict, SortedDict, Splay tree -based dict, etc. Luckily projects such as blist, banyan that implement custom container types do provide copy() method. I don't see why we should make it harder to correctly implement/use custom set/dict types. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22101 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22101] collections.abc.Set doesn't provide copy() method
Guido van Rossum added the comment: You need to learn when to give up. :-) I wasn't the one who added a copy() method to other containers. I personally despise almost all uses of copying (including the entire copy module, both deep and shallow copy functionality). I much prefer to write e.g. list(x) over x.copy() -- when I say list(x) I know the type of the result. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22101 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22101] collections.abc.Set doesn't provide copy() method
Raymond Hettinger added the comment: I don't think this is needed nor do I think that it is a good idea to have a copy() method in the ABCs because they know so little about their concrete underlying class (perhaps the backing store in the filesystem or a database). Besides, a user already has workable alternatives such as creating a new instance and applying |= to populate it. In general, we don't do API expansions without motivating use cases to guide the design. Also, note that MutableMapping does not have a copy method. -- assignee: - rhettinger resolution: - rejected status: open - closed versions: -Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22101 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22101] collections.abc.Set doesn't provide copy() method
Guido van Rossum added the comment: Agreed with Raymond. The return type of copy() for ABCs feels problematic. MutableMapping doesn't have it either. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22101 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22101] collections.abc.Set doesn't provide copy() method
New submission from Akira Li: The documentation for standard types says [1]: clear() and copy() are included for consistency with the interfaces of mutable containers that don’t support slicing operations (such as dict and set) New in version 3.3: clear() and copy() methods. [1] https://docs.python.org/3.4/library/stdtypes.html#immutable-sequence-types but collections.abc documentation mentions only clear() method. I've uploaded a patch that implements Set.copy() method, mentions it in Set's documentation, and adds a sanity test. -- components: Library (Lib) files: set-copy.patch keywords: patch messages: 224255 nosy: akira priority: normal severity: normal status: open title: collections.abc.Set doesn't provide copy() method type: behavior versions: Python 3.4, Python 3.5 Added file: http://bugs.python.org/file36153/set-copy.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22101 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22101] collections.abc.Set doesn't provide copy() method
Changes by Antoine Pitrou pit...@free.fr: -- nosy: +gvanrossum, rhettinger ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22101 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22101] collections.abc.Set doesn't provide copy() method
Changes by Antoine Pitrou pit...@free.fr: -- nosy: +serhiy.storchaka ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22101 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
