Create a property get of 'dict' type

[shineworld 73]

Hi all,

I would like to add, to a python4delphi module, a getter method which return a 'dict'.
For example:

> import pycnccore1 as pyc
>cnc_core = pyc.CNCCore()
>print(cnc_core.paths)
{'user_path': 'c:\\xyz', 'machine_path': 'd:\\machine_test', and so on}

I don't know how to create a Delphi type to contain the dictionary and convert it to a Python dict as a result of the getter method.
 

function TPyCNCCore.GetPaths(AContext: Pointer): PPyObject;
begin
  Adjust(@Self);

  var PathDict: <i_do_not_know>;
  PathDict.Append('user_path', Self.UserPathString);
  PathDict.Append('machine_path', Self.MachinePathString);
  ... and so on ...

  Result := GetPythonEngine.VariantAsPyObject(PathDict);
end;

class procedure TPyCNCCore.RegisterGetSets(PythonType: TPythonType);
begin
  inherited;

  with PythonType do
  begin
    PythonType.AddGetSet('paths', @TPyCNCCore.GetPaths, nil, 'Returns the used paths', nil);
  end;
end;

Thanks in advance for your suggestions
Silverio

[David Heffernan 2345]

Do you want to create a new instance of Python dict every time the property is called? Or aren't you looking to implement the Python mapping protocol so that Python has something that behaves like a dict, but actually just reflects the underlying Delphi object?

[shineworld 73]

In other projects, I've used the automatic conversion of Delphi classes to related Python wrapper classes.

In this project, I would like manually create the python module classes using low-level python implementation.

Looking at P4D WrapFireDac.pas code I saw a way to manually create a dictionary.
Seems to work but is hard to know when to apply Py_XDecRef....

 

function TPyCNCCore.GetPaths(AContext: Pointer): PPyObject;
var
  Key: PPyObject;
  Value: PPyObject;
  PathsDict: PPyObject;
  Engine: TPythonEngine;

  procedure AddItem(const K, V: string);
  begin
    Key := Engine.VariantAsPyObject(Variant(K));
    Value := Engine.VariantAsPyObject(Variant(V));
    Engine.PyDict_SetItem(PathsDict, Key, Value);
    Engine.Py_XDecRef(Key);
    Engine.Py_XDecRef(Value);
  end;

begin
  Adjust(@Self);
  Engine := GetPythonEngine;
  PathsDict := Engine.PyDict_New;
  AddItem('MachineBackupPath', Self.FCNCManager.MachineBackupPath);
  AddItem('MachineCustomizePath', Self.FCNCManager.MachineCustomizePath);
  AddItem('MachineMacrosPath', Self.FCNCManager.MachineMacrosPath);
  AddItem('MachineMediaPath', Self.FCNCManager.MachineMediaPath);
  AddItem('MachinePath', Self.FCNCManager.MachinePath);
  AddItem('MachineRunPath', Self.FCNCManager.MachineRunPath);
  AddItem('MachineVmPath', Self.FCNCManager.MachineVmPath);
  AddItem('SamplesPath', Self.FCNCManager.SamplesPath);
  AddItem('UserDataPath', Self.FCNCManager.UserDataPath);
  Result := PathsDict;
end;

I don't know if this is the right way to 'return' a dict in a getter method..
In my ignorance of the subject, I am navigating by sight.

Should be cool a direct way to convert a TDictionary to Python dict.

Edited April 20, 2023 by shineworld

[David Heffernan 2345]

Consider a large dictionary with, for sake of argument, 1 million items in it. Suppose in Python you wanted to write

 

value = foo[name]

 

Now if foo was actually in your Delphi code, and backed by a Delphi dictionary, do you really want to populate a new Python dict with 1 million items, then perform the lookup in Python, and then throw away that dictionary. Wouldn't it be better to just ask Delphi to perform the lookup. This is what I mean what I talk about the mapping protocol.

 

But it's entirely possible that I have misunderstood what you actually want to do!

[shineworld 73]

3 minutes ago, David Heffernan said:

Considera un grande dizionario con, per amor di discussione, 1 milione di voci al suo interno. Supponiamo che in Python tu voglia scrivere

 

valore = foo[nome]

 

Ora, se foo fosse effettivamente nel tuo codice Delphi e supportato da un dizionario Delphi, vuoi davvero popolare un nuovo dict Python con 1 milione di elementi, quindi esegui la ricerca in Python e poi butta via quel dizionario. Non sarebbe meglio chiedere a Delphi di eseguire la ricerca. Questo è ciò che intendo di ciò che parlo del protocollo di mappatura.

 

Ma è del tutto possibile che io abbia frainteso ciò che realmente vuoi fare!

Ah ok, I completely misrepresented your previous sugestions.

So it would make more sense to do a normal GetPath(name) method that returns the value instead of returning a dictionary with all the variables 🙂

 

It makes sense
Thanks for the suggestion

[pyscripter 689]

48 minutes ago, shineworld said:

Seems to work but is hard to know when to apply Py_XDecRef....

See Passing a python object to a delphi function parameter - Python4Delphi - Delphi-PRAXiS [en] (delphipraxis.net)

 

Edited April 20, 2023 by pyscripter

[David Heffernan 2345]

@pyscripter do you know if it's reasonable to implement the python mapping protocol on the Delphi side so that from python it looks like a Python mapping? 

[pyscripter 689]

1 hour ago, David Heffernan said:

@pyscripter do you know if it's reasonable to implement the python mapping protocol on the Delphi side so that from python it looks like a Python mapping? 

Yes indeed!  P4D makes it quite easy. The TStrings wrapper does that for instance. 

Edited April 20, 2023 by pyscripter