[RF] Implement RooFit::DataError() pythonization in C++

This reduces divergence between the Python and C++ interface.

Tested by the tutorials where this string-to-enum pythonization is used.

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

@@ -194,44 +194,21 @@ def Link(*args, **kwargs):
 
 @cpp_signature("RooFit::DataError(Int_t) ;")
 def DataError(etype):
-    r"""Instead of passing an enum value to this function, you can pass a
-    string with the name of that enum value, for example:
-
-    ~~~ {.py}
-        data.plotOn(frame, DataError="SumW2")
-        # instead of DataError=ROOT.RooAbsData.SumW2
-    ~~~
-
-    If you want to use the `"None"` enum value to disable error plotting, you
+    r"""If you want to use the `"None"` enum value to disable error plotting, you
     can also pass `None` directly instead of passing a string:
 
     ~~~ {.py}
         data.plotOn(frame, DataError=None)
         # instead of DataError="None"
     ~~~
     """
-    # Redefinition of `DataError` to also accept `str` or `NoneType` to get the
-    # corresponding enum values from RooAbsData.DataError.
     from cppyy.gbl import RooFit
 
     # One of the possible enum values is "None", and we want the user to be
     # able to pass None also as a NoneType for convenience.
     if etype is None:
         etype = "None"
 
-    if isinstance(etype, str):
-        try:
-            import ROOT
-
-            etype = getattr(ROOT.RooAbsData.ErrorType, etype)
-        except AttributeError as error:
-            raise ValueError(
-                "Unsupported error type type passed to DataError()."
-                + ' Supported decay types are : "Poisson", "SumW2", "Auto", "Expected", and None.'
-            )
-        except Exception as exception:
-            raise exception
-
     return RooFit._DataError(etype)
 
 

roofit/roofitcore/inc/RooAbsData.h

@@ -106,6 +106,8 @@ class RooAbsData : public TNamed, public RooPrintable {
   virtual double weightSquared() const = 0 ; // DERIVED
 
   enum ErrorType { Poisson, SumW2, None, Auto, Expected } ;
+  static ErrorType errorTypeFromString(std::string const &name);
+
   /// Return the symmetric error on the current weight.
   /// See also weightError(double&,double&,ErrorType) const for asymmetric errors.
   // \param[in] etype Type of error to compute. May throw if not supported.

roofit/roofitcore/inc/RooGlobalFunc.h

@@ -224,6 +224,7 @@ RooCmdArg EventRange(Int_t nStart, Int_t nStop) ;
 // RooChi2Var::ctor / RooNLLVar arguments
 RooCmdArg Extended(bool flag=true) ;
 RooCmdArg DataError(Int_t) ;
+RooCmdArg DataError(std::string const&) ;
 RooCmdArg NumCPU(Int_t nCPU, Int_t interleave=0) ;
 RooCmdArg Parallelize(int nWorkers) ;
 RooCmdArg ModularL(bool flag=false) ;

roofit/roofitcore/src/RooAbsData.cxx

@@ -119,6 +119,9 @@ observable snapshots are stored in the dataset.
 
 #include <iostream>
 #include <memory>
+#include <sstream>
+#include <stdexcept>
+#include <unordered_map>
 
 
 ClassImp(RooAbsData);
@@ -2640,3 +2643,24 @@ TH2F *RooAbsData::createHistogram(const RooAbsRealLValue &var1, const RooAbsReal
 
    return histogram;
 }
+
+////////////////////////////////////////////////////////////////////////////////
+/// Convert a string to the value of the RooAbsData::ErrorType enum with the
+/// same name.
+RooAbsData::ErrorType RooAbsData::errorTypeFromString(std::string const &name)
+{
+   using Map = std::unordered_map<std::string, RooAbsData::ErrorType>;
+   static Map enumMap{{"Poisson", RooAbsData::Poisson},
+                      {"SumW2", RooAbsData::SumW2},
+                      {"None", RooAbsData::None},
+                      {"Auto", RooAbsData::Auto},
+                      {"Expected", RooAbsData::Expected}};
+   auto found = enumMap.find(name);
+   if (found == enumMap.end()) {
+      std::stringstream msg;
+      msg << "Unsupported error type type passed to DataError(). "
+             "Supported decay types are : \"Poisson\", \"SumW2\", \"Auto\", \"Expected\", and None.";
+      throw std::invalid_argument(msg.str());
+   }
+   return found->second;
+}

roofit/roofitcore/src/RooGlobalFunc.cxx

@@ -18,6 +18,7 @@
 
 #include <RooGlobalFunc.h>
 
+#include <RooAbsData.h>
 #include <RooAbsPdf.h>
 #include <RooCategory.h>
 #include <RooDataHist.h>
@@ -469,7 +470,11 @@ RooCmdArg Extended(bool flag)
 }
 RooCmdArg DataError(Int_t etype)
 {
-   return RooCmdArg("DataError", (Int_t)etype, 0, 0, 0, nullptr, nullptr, nullptr, nullptr);
+   return RooCmdArg("DataError", etype);
+}
+RooCmdArg DataError(std::string const &etype)
+{
+   return DataError(RooAbsData::errorTypeFromString(etype));
 }
 RooCmdArg NumCPU(Int_t nCPU, Int_t interleave)
 {