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.mixie@gmail.com> wrote:

Thanks Daniel,

I found my answer here (using your link): https://docs.python.org/3/reference/datamodel.html#preparing-the-class-names...

""" 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 <dfmoisset@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-names... and Pep 3115

On Sat, 3 Nov 2018, 20:55 Joy Diamond <python.gem@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__'])

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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.mixie@gmail.com> wrote:

Thanks Daniel,

I found my answer here (using your link): https://docs.python.org/3/reference/datamodel.html#preparing-the-class-names...

""" 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 <dfmoisset@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-names... and Pep 3115

On Sat, 3 Nov 2018, 20:55 Joy Diamond <python.gem@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/