Fix convert_dtype for empty list and text/ascii spec (#434)

CHANGELOG.md

@@ -1,5 +1,10 @@
 # HDMF Changelog
 
+## HDMF 2.3.0 (Upcoming)
+
+### Bug fixes
+- Fix handling of empty lists against a spec with text/bytes dtype. @rly (#434)
+
 ## HDMF 2.2.0 (August 14, 2020)
 
 ### New features

setup.cfg

@@ -22,7 +22,7 @@ exclude =
   versioneer.py
   src/hdmf/_version.py
 per-file-ignores =
-  docs/gallery/*:E402,
+  docs/gallery/*:E402,T001
   docs/source/tutorials/*:E402
   src/hdmf/__init__.py:F401
   src/hdmf/backends/__init__.py:F401

src/hdmf/build/objectmapper.py

@@ -209,7 +209,13 @@ def convert_dtype(cls, spec, value, spec_dtype=None):
                 ret_dtype = ret.dtype.type
         elif isinstance(value, (tuple, list)):
             if len(value) == 0:
-                return value, spec_dtype_type
+                if spec_dtype_type == _ascii:
+                    ret_dtype = 'ascii'
+                elif spec_dtype_type == _unicode:
+                    ret_dtype = 'utf8'
+                else:
+                    ret_dtype = spec_dtype_type
+                return value, ret_dtype
             ret = list()
             for elem in value:
                 tmp, tmp_dtype = cls.convert_dtype(spec, elem, spec_dtype)

tests/unit/build_tests/test_io_map.py

@@ -1163,6 +1163,11 @@ def test_text_spec(self):
         np.testing.assert_array_equal(ret, np.array(['a', 'b'], dtype='U1'))
         self.assertEqual(ret_dtype, 'utf8')
 
+        value = []
+        ret, ret_dtype = ObjectMapper.convert_dtype(spec, value)
+        self.assertListEqual(ret, value)
+        self.assertEqual(ret_dtype, 'utf8')
+
     def test_ascii_spec(self):
         spec_type = 'ascii'
         spec = DatasetSpec('an example dataset', spec_type, name='data')
@@ -1195,6 +1200,11 @@ def test_ascii_spec(self):
         np.testing.assert_array_equal(ret, value)
         self.assertEqual(ret_dtype, 'ascii')
 
+        value = []
+        ret, ret_dtype = ObjectMapper.convert_dtype(spec, value)
+        self.assertListEqual(ret, value)
+        self.assertEqual(ret_dtype, 'ascii')
+
     def test_no_spec(self):
         spec_type = None
         spec = DatasetSpec('an example dataset', spec_type, name='data')