Support nwb_version as a fixed-length string

CHANGELOG.md

@@ -1,11 +1,13 @@
 # PyNWB Changelog
 
-
 ## PyNWB 2.3.2 (Upcoming)
 
 ### Enhancements and minor changes
 - Fixed typos and added codespell GitHub action to check spelling in the future. @yarikoptic [#1648](https://github.com/NeurodataWithoutBorders/pynwb/pull/1648)
 
+### Bug fixes
+- Fixed bug in ``NWBHDF5IO.nwb_version`` property to support files written by third-party software with a fixed-length ``nwb_version`` attribute. @oruebel [#1669](https://github.com/NeurodataWithoutBorders/pynwb/pull/1669)
+
 ## PyNWB 2.3.1 (February 24, 2023)
 
 ### Bug fixes

src/pynwb/__init__.py

@@ -258,6 +258,11 @@ def nwb_version(self):
         #  or when the HDF5 file is not a valid NWB file
         except KeyError:
             return None, None
+        # Other system may have written nwb_version as a fixed-length string, resulting in a numpy.bytes_ object
+        # on read, rather than a variable-length string. To address this, decode the bytes if necessary.
+        if not isinstance(nwb_version_string, str):
+            nwb_version_string = nwb_version_string.decode()
+
         # Parse the version string
         nwb_version_parts = nwb_version_string.replace("-", ".").replace("_", ".").split(".")
         nwb_version = tuple([int(i) if i.isnumeric() else i

tests/integration/hdf5/test_io.py

@@ -443,6 +443,11 @@ def test_nwb_version_property(self):
             del io.attrs['nwb_version']
         with NWBHDF5IO(self.path, 'r') as io:
             self.assertTupleEqual(io.nwb_version, (None, None))
+        # check that it works when setting the attribute to a fixed-length numpy-bytes string
+        with File(self.path, mode='a') as io:
+            io.attrs['nwb_version'] = np.asarray("2.0.5", dtype=np.bytes_)[()]
+        with NWBHDF5IO(self.path, 'r') as io:
+            self.assertTupleEqual(io.nwb_version, ("2.0.5", (2, 0, 5)))
 
     def test_check_nwb_version_ok(self):
         """Test that opening a current NWBFile passes the version check"""