> On 16 Jun 2017, at 09:46, Nick Coghlan <ncogh...@gmail.com> wrote:
>
> On 16 June 2017 at 07:44, Barry Scott <ba...@barrys-emacs.org> wrote:
>> But I need the result of __dir__ for my object not its base. Then I need to
>> add in the list of member attributes that are missing because python
>> itself has no knowledge of them they are accessed via getattr().
>
> The C code:
>
> dir_result = PyObject_CallMethod(base_type, "__dir__", "O", self);
>
> is roughly equivalent to the Python code:
>
> dir_result = BaseType.__dir__(self)
>
> That is, it's calling the base type's __dir__ method, but it's still
> using the subclass *instance*.
>
> It's the same pattern people use to call a base type's __getattr__ or
> __getattribute__ for the subclass implementation of those methods,
> just without multiple inheritance support (since calling super() from
> C is painful).
Let me show you problem with an example.
Here is an example run of the PyCXX Demo/Python3/simple.cxx code.
: 19:01:15 ~/wc/svn/PyCXX
: [1] barry@Expanse $ PYTHONPATH=obj python3.6
Python 3.6.0 (v3.6.0:41df79263a11, Dec 22 2016, 17:23:13)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import simple
sizeof(int) 4
sizeof(long) 8
sizeof(Py_hash_t) 8
sizeof(Py_ssize_t) 8
>>> dir(simple)
['SimpleError', '__doc__', '__file__', '__loader__', '__name__', '__package__',
'__spec__', 'decode_test', 'derived_class_test', 'encode_test', 'func',
'func_with_callback', 'func_with_callback_catch_simple_error', 'make_instance',
'new_style_class', 'old_style_class', 'var']
>>> n=simple.new_style_class()
new_style_class c'tor Called with 0 normal arguments.
and with 0 keyword arguments:
>>> dir(n)
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__',
'__ge__', '__getattribute__', '__gt__', '__hash__', '__init__',
'__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__',
'__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__',
'__subclasshook__', 'func_keyword', 'func_noargs',
'func_noargs_raise_exception', 'func_varargs', 'func_varargs_call_member']
>>> n.value
'default value'
Notice that 'value' is not in the list of string returned from dir(n).
That omission is because python does not know about 'value'.
The code does this:
Py::Object getattro( const Py::String &name_ )
{
std::string name( name_.as_std_string( "utf-8" ) );
if( name == "value" )
{
return m_value;
}
else
{
return genericGetAttro( name_ );
}
}
Where getattro is called (indirectly) from tp_getattro.
In the python 2 I can tell python that 'value' exists because I provide a value
of __members__.
What is the way to tell python about 'value' in the python3 world?
Barry
>
> Cheers,
> Nick.
>
> --
> Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia
>
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