[Python] Don't rely on heuristic memory policy when passing ownership

bindings/pyroot/pythonizations/python/CMakeLists.txt

@@ -39,6 +39,7 @@ if(roofit)
         ROOT/_pythonization/_roofit/_roojsonfactorywstool.py
         ROOT/_pythonization/_roofit/_roomcstudy.py
         ROOT/_pythonization/_roofit/_roomsgservice.py
+        ROOT/_pythonization/_roofit/_rooplot.py
         ROOT/_pythonization/_roofit/_rooprodpdf.py
         ROOT/_pythonization/_roofit/_roorealvar.py
         ROOT/_pythonization/_roofit/_roosimultaneous.py

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_memory_utils.py

@@ -63,3 +63,28 @@ def _SetDirectory_SetOwnership(self, dir):
         import ROOT
 
         ROOT.SetOwnership(self, False)
+
+
+def declare_cpp_owned_arg(position, name, positional_args, keyword_args, condition=lambda _: True):
+    """
+    Helper function to drop Python ownership of a specific function argument
+    with a given position and name, referring to the C++ signature.
+
+    positional_args and keyword_args should be the usual args and kwargs passed
+    to the function, and condition is an optional condition on which the Python
+    ownership is dropped.
+    """
+    import ROOT
+
+    # has to match the C++ argument name
+    if name in keyword_args:
+        arg = keyword_args[name]
+    elif len(positional_args) > position:
+        arg = positional_args[0]
+    else:
+        # This can happen if the function was called with too few arguments.
+        # In that case we should not do anything.
+        return
+
+    if condition(arg):
+        ROOT.SetOwnership(arg, False)

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_roofit/__init__.py

@@ -40,6 +40,7 @@
 from ._roojsonfactorywstool import RooJSONFactoryWSTool
 from ._roomcstudy import RooMCStudy
 from ._roomsgservice import RooMsgService
+from ._rooplot import RooPlot
 from ._rooprodpdf import RooProdPdf
 from ._roorealvar import RooRealVar
 from ._roosimultaneous import RooSimultaneous
@@ -69,6 +70,7 @@
     RooJSONFactoryWSTool,
     RooMCStudy,
     RooMsgService,
+    RooPlot,
     RooProdPdf,
     RooRealVar,
     RooSimultaneous,

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_roofit/_rooabspdf.py

@@ -31,13 +31,19 @@ def _pack_cmd_args(*args, **kwargs):
     assert len(kwargs) == 0
 
     # Put RooCmdArgs in a RooLinkedList
-    cmdList = ROOT.RooLinkedList()
+    cmd_list = ROOT.RooLinkedList()
     for cmd in args:
         if not isinstance(cmd, ROOT.RooCmdArg):
             raise TypeError("This function only takes RooFit command arguments.")
-        cmdList.Add(cmd)
+        cmd_list.Add(cmd)
 
-    return cmdList
+    # The RooLinkedList passed to functions like fitTo() is expected to be
+    # non-owning. To make sure that the RooCmdArgs live long enough, we attach
+    # them as an attribute of the output list, such that the Python reference
+    # counter doesn't hit zero.
+    cmd_list._owning_pylist = args
+
+    return cmd_list
 
 
 class RooAbsPdf(RooAbsReal):

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_roofit/_rooplot.py

@@ -0,0 +1,19 @@
+# Authors:
+# * Jonas Rembser 09/2023
+################################################################################
+# Copyright (C) 1995-2020, Rene Brun and Fons Rademakers.                      #
+# All rights reserved.                                                         #
+#                                                                              #
+# For the licensing terms see $ROOTSYS/LICENSE.                                #
+# For the list of contributors see $ROOTSYS/README/CREDITS.                    #
+################################################################################
+
+
+class RooPlot(object):
+    def addObject(self, *args, **kwargs):
+        from ROOT._pythonization._memory_utils import declare_cpp_owned_arg
+
+        # Python should transfer the ownership to the RooPlot
+        declare_cpp_owned_arg(0, "obj", args, kwargs)
+
+        return self._addObject(*args, **kwargs)

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_tcollection.py

@@ -93,11 +93,26 @@ def _iter_pyz(self):
         yield o
 
 
+def _TCollection_Add(self, *args, **kwargs):
+    from ROOT._pythonization._memory_utils import declare_cpp_owned_arg
+
+    def condition(_):
+        return self.IsOwner()
+
+    declare_cpp_owned_arg(0, "obj", args, kwargs, condition=condition)
+
+    self._Add(*args, **kwargs)
+
+
 @pythonization('TCollection')
 def pythonize_tcollection(klass):
     # Parameters:
     # klass: class to be pythonized
 
+    # Pythonize Add()
+    klass._Add = klass.Add
+    klass.Add = _TCollection_Add
+
     # Add Python lists methods
     klass.append = klass.Add
     klass.remove = _remove_pyz

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_tgraph.py

@@ -181,6 +181,8 @@
 
 import ROOT
 
+from . import pythonization
+
 
 def set_size(self, buf):
     # Parameters:
@@ -214,3 +216,19 @@ def set_size(self, buf):
 # Add the composite to the list of pythonizors
 ROOT._cppyy.py.add_pythonization(comp)
 
+def _TMultiGraph_Add(self, *args, **kwargs):
+    """
+    The TMultiGraph always takes ownership of the added graphs.
+    """
+    from ROOT._pythonization._memory_utils import declare_cpp_owned_arg
+
+    declare_cpp_owned_arg(0, "graph", args, kwargs)
+
+    self._Add(*args, **kwargs)
+
+
+@pythonization("TMultiGraph")
+def pythonize_tmultigraph(klass):
+    # Pythonizations for TMultiGraph::Add
+    klass._Add = klass.Add
+    klass.Add = _TMultiGraph_Add

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_tseqcollection.py

@@ -241,11 +241,30 @@ def _index_pyz(self, val):
     return idx
 
 
+def _TSeqCollection_AddAt(self, *args, **kwargs):
+    from ROOT._pythonization._memory_utils import declare_cpp_owned_arg
+
+    def condition(_):
+        return self.IsOwner()
+
+    declare_cpp_owned_arg(0, "obj", args, kwargs, condition=condition)
+
+    self._AddAt(*args, **kwargs)
+
+
 @pythonization('TSeqCollection')
 def pythonize_tseqcollection(klass):
+    from ROOT._pythonization._tcollection import _TCollection_Add
+
     # Parameters:
     # klass: class to be pythonized
 
+    # Pythonize Add() methods
+    klass._Add = klass.Add
+    klass.Add = _TCollection_Add
+    klass._AddAt = klass.AddAt
+    klass.AddAt = _TSeqCollection_AddAt
+
     # Item access methods
     klass.__getitem__ = _getitem_pyz
     klass.__setitem__ = _setitem_pyz
@@ -257,3 +276,17 @@ def pythonize_tseqcollection(klass):
     klass.reverse = _reverse_pyz
     klass.sort    = _sort_pyz
     klass.index   = _index_pyz
+
+
+@pythonization("TList")
+def pythonize_tlist(klass):
+    from ROOT._pythonization._tcollection import _TCollection_Add
+
+    # Parameters:
+    # klass: class to be pythonized
+
+    # Pythonize Add() methods
+    klass._Add = klass.Add
+    klass.Add = _TCollection_Add
+    klass._AddAt = klass.AddAt
+    klass.AddAt = _TSeqCollection_AddAt