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How do I free objects after the script execution?#455

AnsweredbyMKostitsyn
MKostitsyn asked this question inQ&A
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I have set of scripts that produce and use objects like this:

from pc1 import Pc as pcrb = pc.ReceiptBuilder()# work with receipt builderrb = None

If I comment the last line, rb seems not to be released automatically.
How can this be avoided?
I would like not to have zombie-objects before I run next script.
I also don't like to be forced to release these objects by hands.

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The following code solves my issue. I hope it will be useful for someone else.
fPyDelphiObjects - is a TDictionary<string, PPyObject>, where I keep all the P4D objects, that were created during script execution.
So this code is kinda my own garbage collector.

I would also appreciate to receive any comments on this method, if it has mistakes or vulnerables.

procedure TDeepyPythonModule.ReleasePyObjects;begin  var aScript := TStringList.Create;  try    var aGlobals := GetPythonEngine.EvalString('globals()');    var aKeys := GetPythonEngine.PyDict_Keys(aGlobals);    try      for var I := 0 to GetPythonEngine.PySequence_Length(aKeys) - 1 do      begin        var aKey := GetPythonEngi…

Replies: 7 comments 4 replies

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Run:
del rb

don't like to be forced to release these objects by hands.

I don't know how to do it automatically

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1 reply
@MKostitsyn
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rb = None also works fine, but I do want to do it automatically.

In my Delphi project I have list of produced PyObjects, but of course I don't know names of the variables that store them.
Now I think, GlobalVars/LocalVars dictionaries could help me somehow.

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AFAIRrb = None only zeros the pointer to the var. But value of var is kept.

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The following code solves my issue. I hope it will be useful for someone else.
fPyDelphiObjects - is a TDictionary<string, PPyObject>, where I keep all the P4D objects, that were created during script execution.
So this code is kinda my own garbage collector.

I would also appreciate to receive any comments on this method, if it has mistakes or vulnerables.

procedure TDeepyPythonModule.ReleasePyObjects;begin  var aScript := TStringList.Create;  try    var aGlobals := GetPythonEngine.EvalString('globals()');    var aKeys := GetPythonEngine.PyDict_Keys(aGlobals);    try      for var I := 0 to GetPythonEngine.PySequence_Length(aKeys) - 1 do      begin        var aKey := GetPythonEngine.PySequence_GetItem(aKeys, I);        if aKey <> nil then        try          var aValue := GetPythonEngine.PyDict_GetItem(aGlobals, aKey);          for var aPair in fPyDelphiObjects do            if aPair.Value = aValue then            begin              var aKeyStr := GetPythonEngine.PyUnicodeAsString(aKey);              aScript.Add('del ' + aKeyStr);              Break;            end;        finally          GetPythonEngine.Py_DECREF(aKey);        end;      end;    finally      GetPythonEngine.Py_xDECREF(aKeys);      GetPythonEngine.Py_xDECREF(aGlobals);    end;    if aScript.Count > 0 then      GetPythonEngine.ExecStrings(aScript);  finally    FreeAndNil(aScript);  end;end;
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Answer selected byMKostitsyn
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here is how to get globals w/o calculating 'globals()'

procedure TAppPython.InitModuleMain;begin  with FEngine do    if ModuleMain=nil then    begin      ModuleMain:= PyImport_AddModule('__main__'); //same as PythonEngine.GetMainModule      if ModuleMain=nil then        raise EPythonError.Create('Python: cannot init __main__');      if GlobalsMain=nil then        GlobalsMain:= PyModule_GetDict(ModuleMain);    end;end;
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@MKostitsyn
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Why is it better? Will it save a lot of resources?

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also: you call GetPythonEngine 10 times. cache it to var.

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also:
seehttps://stackoverflow.com/questions/21514631/how-to-delete-an-instantiated-object-python
If i got the idea: running 'del x' is the same as calling DLL API: which decreases ref count. Py_xDECREF .

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@MKostitsyn
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This was my first shot - just to iterate the fPyDelphiObjects dict and to decrease the reference counter, but it lead to the AV in the following scripts when using the same variable.
It seems, Python Engine did not know, that the object was already released.

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I have set of scripts that produce and use objects like this:

from pc1 import Pc as pcrb = pc.ReceiptBuilder()# work with receipt builderrb = None

If I comment the last line, rb seems not to be released automatically. How can this be avoided? I would like not to have zombie-objects before I run next script. I also don't like to be forced to release these objects by hands.

You can change your code to the following so that you do not pollute the main module dictionary.

defdowork():frompc1importPcaspcrb=pc.ReceiptBuilder()# work with receipt builderdowork()
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@MKostitsyn
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I'm just a beginner in Python.
Is this approach suitable for any possible scenario? For example with local functions/classes/threads, with importing libraries, and so on and so on?

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