Python Programming On Win32

Extending Python with a Delphi DLL

It’s easy to create a DLL in Delphi and expose it as a Python module. Let’s start with one of the PyDelphi tutorial examples, then extend it into something more useful. The initial example exports one function to add two numbers together. In Delphi, choose File → New → DLL to create a DLL project, and save it. Then create a new Pascal module (called just module.pas) containing the following code:

unit module;

interface
uses PythonEngine;

procedure initdemodll; cdecl;
var
  gEngine : TPythonEngine;
  gModule : TPythonModule;

implementation

function Add( Self, Args : PPyObject ) : PPyObject; far; cdecl;
var
  a, b : Integer;
begin
  with GetPythonEngine do
    begin
      if PyArg_ParseTuple( args, 'ii:Add', [@a, @b] ) <> 0 then
        begin
          Result := PyInt_FromLong( a + b );
        end
      else
        Result := nil;
    end;
end;

procedure initdemodll;
begin
  try
    gEngine := TPythonEngine.Create(nil);
    gEngine.AutoFinalize := False;
    gEngine.LoadDll;
    gModule := TPythonModule.Create(nil);
    gModule.Engine := gEngine;
    gModule.ModuleName := 'demodll';
    gModule.AddMethod( 'add', @Add, 'add(a,b) -> a+b' );
    gModule.Initialize;
  except
  end;
end;

initialization
finalization
  gEngine.Free;
  gModule.Free;
  frmAbout.Free;
end.

You can see the similarity between this and the minimal C extension earlier in the chapter. However, PyDelphi includes a TPythonModule component that slightly changes the initialization of the Python function names. Having written this, you can edit the Delphi project file (extension DPR) to ...