Add python bindings for the RNTuple backend (#488)

* Add RNTupleReader to python bindings and file dispatch

* Complete ROOTNTupleReader interface and expose it in dictionaries

* Add python bindings for RNTuple writer

include/podio/ROOTNTupleReader.h

@@ -9,6 +9,7 @@
 #include "podio/utilities/DatamodelRegistryIOHelpers.h"
 
 #include <string>
+#include <string_view>
 #include <unordered_map>
 #include <vector>
 
@@ -47,6 +48,9 @@ class ROOTNTupleReader {
    */
   std::unique_ptr<podio::ROOTFrameData> readEntry(const std::string& name, const unsigned entry);
 
+  /// Get the names of all the available Frame categories in the current file(s)
+  std::vector<std::string_view> getAvailableCategories() const;
+
   /// Returns number of entries for the given name
   unsigned getEntries(const std::string& name);
 
@@ -55,6 +59,16 @@ class ROOTNTupleReader {
     return m_fileVersion;
   }
 
+  /// Get the datamodel definition for the given name
+  const std::string_view getDatamodelDefinition(const std::string& name) const {
+    return m_datamodelHolder.getDatamodelDefinition(name);
+  }
+
+  /// Get all names of the datamodels that ara available from this reader
+  std::vector<std::string> getAvailableDatamodels() const {
+    return m_datamodelHolder.getAvailableDatamodels();
+  }
+
   void closeFile();
 
 private:

python/podio/reading.py

@@ -23,11 +23,26 @@ def _is_frame_sio_file(filename):
                      'or there is a version mismatch')
 
 
-def _is_frame_root_file(filename):
-  """Peek into the root file to determine whether this is a legacy file or not."""
+class RootFileFormat:
+  """Enum to specify the ROOT file format"""
+  TTREE = 0  # Non-legacy TTree based file
+  RNTUPLE = 1  # RNTuple based file
+  LEGACY = 2  # Legacy TTree based file
+
+
+def _determine_root_format(filename):
+  """Peek into the root file to determine which flavor we have at hand."""
   file = TFile.Open(filename)
-  # The ROOT Frame writer puts a podio_metadata TTree into the file
-  return bool(file.Get('podio_metadata'))
+
+  metadata = file.Get("podio_metadata")
+  if not metadata:
+    return RootFileFormat.LEGACY
+
+  md_class = metadata.IsA().GetName()
+  if "TTree" in md_class:
+    return RootFileFormat.TTREE
+
+  return RootFileFormat.RNTUPLE
 
 
 def get_reader(filename):
@@ -50,8 +65,12 @@ def get_reader(filename):
     return sio_io.LegacyReader(filename)
 
   if filename.endswith('.root'):
-    if _is_frame_root_file(filename):
+    root_flavor = _determine_root_format(filename)
+    if root_flavor == RootFileFormat.TTREE:
       return root_io.Reader(filename)
-    return root_io.LegacyReader(filename)
+    if root_flavor == RootFileFormat.RNTUPLE:
+      return root_io.RNTupleReader(filename)
+    if root_flavor == RootFileFormat.LEGACY:
+      return root_io.LegacyReader(filename)
 
   raise ValueError('file must end on .root or .sio')

python/podio/root_io.py

@@ -27,6 +27,24 @@ def __init__(self, filenames):
     super().__init__()
 
 
+class RNTupleReader(BaseReaderMixin):
+  """Reader class for reading podio RNTuple root files."""
+
+  def __init__(self, filenames):
+    """Create an RNTuple reader that reads from the passed file(s).
+
+    Args:
+        filenames (str or list[str]): file(s) to open and read data from
+    """
+    if isinstance(filenames, str):
+      filenames = (filenames,)
+
+    self._reader = podio.ROOTNTupleReader()
+    self._reader.openFiles(filenames)
+
+    super().__init__()
+
+
 class LegacyReader(BaseReaderMixin):
   """Reader class for reading legacy podio root files.
 
@@ -59,3 +77,14 @@ def __init__(self, filename):
         filename (str): The name of the output file
     """
     self._writer = podio.ROOTFrameWriter(filename)
+
+
+class RNTupleWriter(BaseWriterMixin):
+  """Writer class for writing podio root files"""
+  def __init__(self, filename):
+    """Create a writer for writing files
+
+    Args:
+        filename (str): The name of the output file
+    """
+    self._writer = podio.ROOTNTupleWriter(filename)

src/ROOTNTupleReader.cc

@@ -87,6 +87,7 @@ void ROOTNTupleReader::openFiles(const std::vector<std::string>& filenames) {
 
   auto edmView = m_metadata->GetView<std::vector<std::tuple<std::string, std::string>>>(root_utils::edmDefBranchName);
   auto edm = edmView(0);
+  m_datamodelHolder = DatamodelDefinitionHolder(std::move(edm));
 
   auto availableCategoriesField = m_metadata->GetView<std::vector<std::string>>(root_utils::availableCategories);
   m_availableCategories = availableCategoriesField(0);
@@ -107,6 +108,15 @@ unsigned ROOTNTupleReader::getEntries(const std::string& name) {
   return m_totalEntries[name];
 }
 
+std::vector<std::string_view> ROOTNTupleReader::getAvailableCategories() const {
+  std::vector<std::string_view> cats;
+  cats.reserve(m_availableCategories.size());
+  for (const auto& cat : m_availableCategories) {
+    cats.emplace_back(cat);
+  }
+  return cats;
+}
+
 std::unique_ptr<ROOTFrameData> ROOTNTupleReader::readNextEntry(const std::string& name) {
   return readEntry(name, m_entries[name]);
 }

src/ROOTNTupleWriter.cc

@@ -164,6 +164,10 @@ std::unique_ptr<ROOT::Experimental::RNTupleModel>
 ROOTNTupleWriter::createModels(const std::vector<StoreCollection>& collections) {
   auto model = ROOT::Experimental::RNTupleModel::CreateBare();
   for (auto& [name, coll] : collections) {
+    // For the first entry in each category we also record the datamodel
+    // definition
+    m_datamodelCollector.registerDatamodelDefinition(coll, name);
+
     const auto collBuffers = coll->getBuffers();
 
     if (collBuffers.vecPtr) {
@@ -252,7 +256,7 @@ void ROOTNTupleWriter::finish() {
   auto edmDefinitions = m_datamodelCollector.getDatamodelDefinitionsToWrite();
   auto edmField =
       m_metadata->MakeField<std::vector<std::tuple<std::string, std::string>>>(root_utils::edmDefBranchName);
-  *edmField = edmDefinitions;
+  *edmField = std::move(edmDefinitions);
 
   auto availableCategoriesField = m_metadata->MakeField<std::vector<std::string>>(root_utils::availableCategories);
   for (auto& [c, _] : m_categories) {

src/root_selection.xml

@@ -3,5 +3,7 @@
     <class name="podio::ROOTFrameReader"/>
     <class name="podio::ROOTLegacyReader"/>
     <class name="podio::ROOTFrameWriter"/>
+    <class name="podio::ROOTNTupleReader"/>
+    <class name="podio::ROOTNTupleWriter"/>
   </selection>
 </lcgdict>

tests/dumpmodel/CMakeLists.txt

@@ -57,10 +57,43 @@ if (ENABLE_SIO)
     )
 endif()
 
+set(rntuple_roundtrip_tests "")
+if (ENABLE_RNTUPLE)
+  add_test(NAME datamodel_def_store_roundtrip_rntuple COMMAND
+    ${PROJECT_SOURCE_DIR}/tests/scripts/dumpModelRoundTrip.sh
+    ${PROJECT_BINARY_DIR}/tests/root_io/example_rntuple.root
+    datamodel
+    ${PROJECT_SOURCE_DIR}/tests
+  )
+  PODIO_SET_TEST_ENV(datamodel_def_store_roundtrip_rntuple)
+
+  add_test(NAME datamodel_def_store_roundtrip_rntuple_extension COMMAND
+    ${PROJECT_SOURCE_DIR}/tests/scripts/dumpModelRoundTrip.sh
+    ${PROJECT_BINARY_DIR}/tests/root_io/example_rntuple.root
+    extension_model
+    ${PROJECT_SOURCE_DIR}/tests/extension_model
+    --upstream-edm=datamodel:${PROJECT_SOURCE_DIR}/tests/datalayout.yaml
+  )
+  PODIO_SET_TEST_ENV(datamodel_def_store_roundtrip_rntuple_extension)
+
+  set(rntuple_roundtrip_tests
+    datamodel_def_store_roundtrip_rntuple
+    datamodel_def_store_roundtrip_rntuple_extension
+  )
+
+  set_tests_properties(
+      ${rntuple_roundtrip_tests}
+    PROPERTIES
+      DEPENDS write_rntuple
+  )
+
+endif()
+
 set_tests_properties(
     datamodel_def_store_roundtrip_root
     datamodel_def_store_roundtrip_root_extension
     ${sio_roundtrip_tests}
+    ${rntuple_roundtrip_tests}
   PROPERTIES
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
   )

tests/root_io/CMakeLists.txt

@@ -19,6 +19,7 @@ if(ENABLE_RNTUPLE)
       ${root_dependent_tests}
       write_rntuple.cpp
       read_rntuple.cpp
+      read_python_frame_rntuple.cpp
      )
 endif()
 set(root_libs TestDataModelDict ExtensionDataModelDict podio::podioRootIO)
@@ -80,6 +81,13 @@ endforeach()
 
 #--- Write via python and the ROOT backend and see if we can read it back in in
 #--- c++
-add_test(NAME write_python_frame_root COMMAND python3 ${PROJECT_SOURCE_DIR}/tests/write_frame.py example_frame_with_py.root)
+add_test(NAME write_python_frame_root COMMAND python3 ${PROJECT_SOURCE_DIR}/tests/write_frame.py example_frame_with_py.root root_io.Writer)
 PODIO_SET_TEST_ENV(write_python_frame_root)
 set_property(TEST read_python_frame_root PROPERTY DEPENDS write_python_frame_root)
+
+if (ENABLE_RNTUPLE)
+  add_test(NAME write_python_frame_rntuple COMMAND python3 ${PROJECT_SOURCE_DIR}/tests/write_frame.py example_frame_with_py_rntuple.root root_io.RNTupleWriter)
+  PODIO_SET_TEST_ENV(write_python_frame_rntuple)
+
+  set_property(TEST read_python_frame_rntuple PROPERTY DEPENDS write_python_frame_rntuple)
+endif()

tests/root_io/read_python_frame_rntuple.cpp

@@ -0,0 +1,7 @@
+#include "read_python_frame.h"
+
+#include "podio/ROOTNTupleReader.h"
+
+int main() {
+  return read_frame<podio::ROOTNTupleReader>("example_frame_with_py_rntuple.root");
+}

tests/sio_io/CMakeLists.txt

@@ -40,6 +40,6 @@ set_property(TEST check_benchmark_outputs_sio PROPERTY DEPENDS read_timed_sio wr
 
 #--- Write via python and the SIO backend and see if we can read it back in in
 #--- c++
-add_test(NAME write_python_frame_sio COMMAND python3 ${PROJECT_SOURCE_DIR}/tests/write_frame.py example_frame_with_py.sio)
+add_test(NAME write_python_frame_sio COMMAND python3 ${PROJECT_SOURCE_DIR}/tests/write_frame.py example_frame_with_py.sio sio_io.Writer)
 PODIO_SET_TEST_ENV(write_python_frame_sio)
 set_property(TEST read_python_frame_sio PROPERTY DEPENDS write_python_frame_sio)

tests/write_frame.py

@@ -54,13 +54,14 @@ def create_frame():
   return frame
 
 
-def write_file(io_backend, filename):
+def write_file(writer_type, filename):
   """Write a file using the given Writer type and put one Frame into it under
   the events category
   """
+  io_backend, writer_name = writer_type.split(".")
   io_module = importlib.import_module(f"podio.{io_backend}")
 
-  writer = io_module.Writer(filename)
+  writer = getattr(io_module, writer_name)(filename)
   event = create_frame()
   writer.write_frame(event, "events")
 
@@ -70,9 +71,10 @@ def write_file(io_backend, filename):
 
   parser = argparse.ArgumentParser()
   parser.add_argument("outputfile", help="Output file name")
+  parser.add_argument("writer", help="The writer type to use")
 
   args = parser.parse_args()
 
   io_format = args.outputfile.split(".")[-1]
 
-  write_file(f"{io_format}_io", args.outputfile)
+  write_file(args.writer, args.outputfile)

tools/CMakeLists.txt

@@ -37,4 +37,9 @@ if(BUILD_TESTING)
     CREATE_DUMP_TEST(podio-dump-detailed-sio-legacy "write_sio" --detailed --entries 9 ${PROJECT_BINARY_DIR}/tests/sio_io/example.sio)
   endif()
 
+  if (ENABLE_RNTUPLE)
+    CREATE_DUMP_TEST(podio-dump-rntuple "write_rntuple" ${PROJECT_BINARY_DIR}/tests/root_io/example_rntuple.root)
+    CREATE_DUMP_TEST(podio-dump-rntuple-detailed "write_rntuple" --detailed --category events --entries 1:3 ${PROJECT_BINARY_DIR}/tests/root_io/example_rntuple.root)
+  endif()
+
 endif()