I think the documentation is correct but you misinterpreted the intent of that code. The code you're quoting, which is an example, is not about ending up with a custom dict within the instance, the intent of the author was just to captur the memeber_names list. So what it does for that is customizing the class dict in prepare(), but then in __init__ it *intentionally* converts it to a regular dict after extracting the member_names. The goal of the example is ending up with instances with regular attribute dicts but an extra member_names attributes, while I think that you're looking for to end up with a custom attribute dict (so in *your* case, you do not need to do the copying)
On Sun, 4 Nov 2018 at 00:03, Amit Green <amit.mi...@gmail.com> wrote: > Thanks Daniel, > > I found my answer here (using your link): > https://docs.python.org/3/reference/datamodel.html#preparing-the-class-namespace > > """ > When a new class is created by type.__new__, the object provided as the > namespace parameter is copied to a new ordered mapping and the original > object is discarded. > """ > > Therefore the answer seems to be that > https://www.python.org/dev/peps/pep-3115/ needs to be updated & fixed. > > Replace the following: > > """ > > def __new__(cls, name, bases, classdict): > # Note that we replace the classdict with a regular > # dict before passing it to the superclass, so that we > # don't continue to record member names after the class > # has been created. > result = type.__new__(cls, name, bases, dict(classdict)) > result.member_names = classdict.member_names > return result > > """ > > With: > > """ > def __new__(cls, name, bases, classdict): > > result = type.__new__(cls, name, bases, classdict) > result.member_names = classdict.member_names > return result > > """ > > Removing the incorrect comments & the copying of `classdict` > > I will go file a bug report to that effect. > > Thanks, > > Joy Diamond. > > > > On Sat, Nov 3, 2018 at 7:55 PM Daniel Moisset <dfmois...@gmail.com> wrote: > >> If I understood correctly what you want, it's possible with a metaclass. >> Check the __prepare__ method at >> https://docs.python.org/3/reference/datamodel.html#preparing-the-class-namespace >> and Pep 3115 >> >> On Sat, 3 Nov 2018, 20:55 Joy Diamond <python....@gmail.com wrote: >> >>> Team, >>> >>> Are we supposed to be able to have our own class dictionary in python 3? >>> >>> If we currently cannot -- do we want to be able to? >>> >>> That we can have out own class dictionary in python 3 is strongly >>> implied in the following at https://www.python.org/dev/peps/pep-3115/ >>> where it says: >>> >>> """ >>> >>> # The metaclass invocation >>> def __new__(cls, name, bases, classdict): >>> # Note that we replace the classdict with a regular >>> # dict before passing it to the superclass, so that we >>> # don't continue to record member names after the class >>> # has been created. >>> result = type.__new__(cls, name, bases, dict(classdict)) >>> result.member_names = classdict.member_names >>> return result >>> >>> """ >>> >>> I don't understand this. As far as I can tell, no matter what class >>> dictionary you pass into `type.__new__` it creates a copy of it. >>> >>> Am I missing something? Is this supposed to work? Is the documentation >>> wrong? >>> >>> Thanks, >>> >>> Joy Diamond. >>> >>> Program that shows that the class dictionary created is not what we pass >>> in --- Shows the actual symbol table is `dict` not `SymbolTable` >>> >>> class SymbolTable(dict): >>> pass >>> >>> members = SymbolTable(a = 1) >>> >>> X = type('X', ((object,)), members) >>> >>> members['b'] = 2 >>> >>> print('X.a: {}'.format(X.a)) >>> >>> try: >>> print('X.b: {}'.format(X.b)) >>> except AttributeError as e: >>> print('X.b: does not exist') >>> >>> # >>> # Get the actual symbol table of `X`, bypassing the mapping proxy. >>> # >>> X__symbol_table = __import__('gc').get_referents(X.__dict__)[0] >>> >>> print('The type of the actual symbol table of X is: {} with keys: >>> {}'.format( >>> type(X__symbol_table), >>> X__symbol_table.keys())) >>> >>> >>> # Prints out >>> # X.a: 1 >>> # X.b: does not exist >>> # The type of the actual symbol table of X is: <class 'dict'> with keys: >>> dict_keys(['a', '__module__', '__dict__', '__weakref__', '__doc__']) >>> >>> >>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon> >>> Virus-free. >>> www.avast.com >>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link> >>> <#m_7342312465347859571_m_3863327966708087084_m_7370047320667964513_m_603818574152564677_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> >>> _______________________________________________ >>> Python-ideas mailing list >>> Python-ideas@python.org >>> https://mail.python.org/mailman/listinfo/python-ideas >>> Code of Conduct: http://python.org/psf/codeofconduct/ >>> >>
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