FindingPython

How Python for Delphi finds your Python distribution in Windows

To use Python for Delphi you need to download and install python. There are a number of different python distributions, the most common ones being from www.python.org or the Anaconda distribution used for data analytics.

Registered versus unregistered vesions

When you install Python in Windows, you have the option to register it, either for all users or for the current user. Registration involves writing information to the registry about the location of the installation, the name and location of the help file etc.

Setting the properties of PythonEngine

• If you want to use the latest registered Python version installed
  • Set UseLastKnownVerion property to True
• If you want a specific registered version you need to set the following properties:
  • DLLName e.g. python38.dll
  • RegVersion e.g 3.8
  • Set UseLastKnownVerion property to False
• If you want to use a specific unregistered version set the following properties
  • DLLName e.g. python38.dll
  • RegVersion e.g 3.8
  • Set UseLastKnownVerion property to False
  • Set the DLLPath to the path where the DLL is located
  • Set the AutoLoad property to False
  • Add the following statement to the PythonEngine OnBeforeLoad event handler, assuming that PythonEngine is the name of the component

    PythonEngine.SetPythonHome('your python installation directory')

  • Add the following statement to your FormCreate handler:

    PythonEngine.LoadDll;

Notes:

• 32-bit Delphi applications only work with 32-versions of Python and 64-bit Delphi applications only work with 64-bit versions of Python.
• Anaconda distributions require that you call SetPythonHome even if they are registered.

Using the PythonVersions unit

The PythonVersion unit can help to find and load the python version you want correctly. It deals with various complications such as registred/unregistred versions, Anaconda distributions and virtual environments. To use it set the Autoload property of PythonEngine to False and then in your FormCreate load python as follows:

  var PythonVersion: TPythonVersion

  if GetRegisteredPythonVersion(SysVersion, PythonVersion) then
  or
  if PythonVersionFromPath(Path, PythonVersion) then
  begin
    PythonVersion.AssignTo(PythonEngine)
    PythonEngine.LoadDLL
  end
  else 

Here is the TPythonVersion.AssignTo procedure:

procedure TPythonVersion.AssignTo(PythonEngine: TPersistent);
begin
  if PythonEngine is TPythonEngine then
  begin
    TPythonEngine(PythonEngine).UseLastKnownVersion := False;
    TPythonEngine(PythonEngine).RegVersion := SysVersion;
    TPythonEngine(PythonEngine).DllName := DLLName;
    TPythonEngine(PythonEngine).DllPath := DLLPath;
    TPythonEngine(PythonEngine).APIVersion := ApiVersion;
    if Is_venv then begin
      TPythonEngine(PythonEngine).VenvPythonExe := PythonExecutable;
      TPythonEngine(PythonEngine).SetPythonHome(DLLPath);
    end else if not IsRegistered or Is_conda then
      { 
         Not sure why but PythonHome needs to be set even for
         registered conda distributions
         Note also that for conda distributions to work properly,
         you need to add Format('%s;%0:s\Library\bin;', [Version.InstallPath]
         to your Windows path if it is not there already.
      }
      TPythonEngine(PythonEngine).SetPythonHome(InstallPath);
  end;
end;

See also: Masking FPU Exceptions