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

src/pynwb/file.py

@@ -549,6 +549,30 @@ def objects(self):
             self.all_children()
         return self.__obj
 
+    @docval({'name': 'neurodata_types', 'type': (type, str),
+             'doc': ('The PyNWB container class to search for instances of, or the string with the name of '
+                     'the neurodata_type')},)
+    def find_all(self, neurodata_type):
+        """Return all PyNWB objects in the file that are instances of the neurodata_type class.
+
+        This includes objects that are instances of a subclass of the class. A string with the name of the
+        neurodata_type can also be passed in.
+
+        .. code-block:: python
+
+            from pynwb import ImageSeries
+            obj_list = find_all(nwbfile, ImageSeries)
+            obj_list = find_all(nwbfile, "EcephysSpecimen")  # EcephysSpecimen is defined in a loaded extension
+
+        """
+        if isinstance(neurodata_type, str):
+            pynwb_cls = self.io.manager.type_map.get_dt_container_cls(neurodata_type)
+        else:
+            pynwb_cls = neurodata_type
+
+        ret = [obj for obj in self.objects.values() if isinstance(obj, pynwb_cls)]
+        return ret
+
     @property
     def modules(self):
         warn("NWBFile.modules has been replaced by NWBFile.processing.", DeprecationWarning)