simple2 demo seems to be buggy

[π <sun...@gm...>]

I've been playing around with PyCXX, slowly figuring it out.

I've got all of the demos but one working: simple, example, range, iter, but not simple2.

The following code shows the problem, I think:

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import simple2
import sys

print( "---" )
print( id(simple2.xxx.second) ) # 4299353944
print( id(simple2.xxx.second) ) # 4299353944
print( id(simple2.xxx.second) ) # 4299353944
print( "---" )

a,b,c = simple2.xxx.second, simple2.xxx.second, simple2.xxx.second
print( id(a) ) # 4299353944
print( id(b) ) # 4299513704
print( id(c) ) # 4299214952
print( "---" )
print( id(simple2.xxx.second) ) # 4299435416
print( id(simple2.xxx.second) ) # 4299435416
print( id(simple2.xxx.second) ) # 4299435416
print( "---" )

p = simple2.xxx.second
q = simple2.xxx.second

print ( id(p) ) # 4299435416
print ( id(q) ) # 4299521272

print( id(simple2.xxx.second) ) # 4299516904
print( id(simple2.xxx.second) ) # 4299516904
print( "---" )

print ( "Making dict m..." )
m = {
    simple2.xxx.first  : 1,
    simple2.xxx.second : 2,
    simple2.xxx.third  : 3
}

print( "---" )
print( id(simple2.xxx.second) )  # 4299381256
print( id(simple2.xxx.second) )  # 4299381256
print( "---" )

print ( "... done!" )

v = m[ simple2.xxx.second ]

#Traceback (most recent call last):
#    File "./py/test_simple2.py", line 53, in <module>
#    v = m[ simple2.xxx.second ]
#
#did EnumString< xxx_t >::EnumString()
#KeyError: <xxx.second>
#-1
#Program ended with exit code: 0

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It looks as though every time we assign simple2.xxx.second to some variable, it creates a new instance rather than giving just a new reference.

And that in defining m = {…}, a new instance is also created.

If instead we were to do:

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u = simple2.xxx.second
m = {
    simple2.xxx.first  : 1,
    u : 2,
    simple2.xxx.third  : 3
}
v = m[ u ]
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… this works.

The same problem doesn't seem to occur with the root object:
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print( id(simple2.xxx) )
print( id(simple2.xxx) )
      
x1 = simple2.xxx
x2 = simple2.xxx
print( id(x1) )
print( id(x2) )
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The above produces the same id all 4 times.

I think the problem is here:
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    // if the given string has an associated T object, return that T object
    Py::Object getattr( const char *_name ) override
    {
        std::string name( _name );
        T value;

        if( name == "__methods__" )
            return Py::List();

        if( name == "__members__" )
            return memberList( static_cast<T>( 0 ) );

        if( toEnum( name, value ) ) // <-- sets value
            return Py::asObject( new pysvn_enum_value<T>( value ) ); // <— HERE

        return this->getattr_methods( _name );    
    }
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Where it can be seen clearly that getattr returns a newly created Python object.

In fact I think that the only time we ever get the same id returned consecutively is due to coincidence: the first object gets destructed, and another object gets created. If this happen straight away, maybe the Python runtime reuses the ID of the object that just got destroyed.

Although I still don't fully grok this simple2 example (I don't find it very simple at all), my guess is that to fix this it would be necessary to create a pysvn_enum_value<xxx_t> py-extension-object for each xxx_t enum value, and bind them together using ‘map’ upon creation of simple.xxx (i.e. in it’s init_type).  Then whenever e.g. xxx.simple2.second is encountered, get_attr can return a non-owned reference to the corresponding pysvn_enum_value<xxx_t>.

Another thing I notice is that several functions contain:

    static EnumString<T> enum_map;

This doesn't look like a good idea, surely there should only be one map created.  Maybe it should be a static public variable inside EnumString?

π