Add methods to find objects of a given neurodata type / pynwb class

src/pynwb/__init__.py

@@ -349,6 +349,35 @@ def export(self, **kwargs):
         kwargs['container'] = nwbfile
         super().export(**kwargs)
 
+    @docval({'name': 'neurodata_type', 'type': str, 'doc': 'The neurodata type to search for.'},
+            {'name': 'namespace', 'type': str, 'doc': 'The namespace of the neurodata type to search for.'},)
+    def get_neurodata_type_objs(self, neurodata_type: str, namespace: str):
+        """Return all PyNWB objects in the file that have a neurodata type from a namespace.
+
+        This works regardless of whether the extension was imported earlier in the python execution.
+
+        This method is useful for getting neurodata type objects from cached extensions where you
+        do not have easy access to a python class to pass to `NWBFile.find_all_of_class`.
+
+        All objects that are instances of the class associated with the given neurodata_type in the
+        given namespace will be returned. This includes objects that are instances of a subclass.
+
+        For example, if an extension defines a new neurodata type OnePhotonSeries that extends
+        ImageSeries, then `get_neurodata_type_objects_in_file(io, "ImageSeries", "core")` will
+        include all OnePhotonSeries objects.
+
+        .. code-block:: python
+
+            from pynwb import NWBHDF5IO
+            with NWBHDF5IO(filepath, mode="r", load_namespaces=True) as io:
+                obj_list = io.get_neurodata_type_objs("Subject", "core")
+
+        """
+        pynwb_cls = self.manager.type_map.get_dt_container_cls(neurodata_type, namespace)
+
+        read_nwbfile = self.read()
+        return read_nwbfile.find_all_of_class(pynwb_cls)
+
 
 from . import io as __io  # noqa: F401,E402
 from .core import NWBContainer, NWBData  # noqa: F401,E402

src/pynwb/file.py

@@ -549,6 +549,21 @@ def objects(self):
             self.all_children()
         return self.__obj
 
+    @docval({'name': 'pynwb_class', 'type': type, 'doc': 'The PyNWB class to search for instances of.'},)
+    def find_all_of_class(self, pynwb_class: type):
+        """Return all PyNWB objects in the file that are instances of the pynwb_class class.
+
+        This includes objects that are instances of a subclass of the class.
+
+        .. code-block:: python
+
+            from pynwb import ImageSeries
+            obj_list = get_neurodata_type_objects(nwbfile, ImageSeries)
+
+        """
+        ret = [obj for obj in self.objects.values() if isinstance(obj, pynwb_class)]
+        return ret
+
     @property
     def modules(self):
         warn("NWBFile.modules has been replaced by NWBFile.processing.", DeprecationWarning)