Fix issue with empty array colnames for DynamicTable (#379)

CHANGELOG.md

@@ -1,5 +1,11 @@
 # HDMF Changelog
 
+## HDMF 1.6.4 (Upcoming)
+
+### Bug fixes:
+- Fix validation of empty arrays and scalar attributes. @rly (#377)
+- Fix issue with constructing `DynamicTable` with empty array colnames. @rly (#379)
+
 ## HDMF 1.6.3 (June 9, 2020)
 
 ### Internal improvements

src/hdmf/backends/hdf5/h5tools.py

@@ -497,7 +497,7 @@ def __read_dataset(self, h5obj, name=None):
                 kwargs["data"] = scalar
         elif ndims == 1:
             d = None
-            if h5obj.dtype.kind == 'O':
+            if h5obj.dtype.kind == 'O' and len(h5obj) > 0:
                 elem1 = h5obj[0]
                 if isinstance(elem1, (str, bytes)):
                     d = h5obj

src/hdmf/common/table.py

@@ -255,11 +255,13 @@ def __init__(self, **kwargs):  # noqa: C901
 
         self.id = id
 
-        if colnames is None:
+        # NOTE: self.colnames and self.columns are always tuples
+        # if kwarg colnames is an h5dataset, self.colnames is still a tuple
+        if colnames is None or len(colnames) == 0:
             if columns is None:
                 # make placeholder for columns if nothing was given
-                self.colnames = list()
-                self.columns = list()
+                self.colnames = tuple()
+                self.columns = tuple()
             else:
                 # Figure out column names if columns were given
                 tmp = list()
@@ -268,7 +270,7 @@ def __init__(self, **kwargs):  # noqa: C901
                         continue
                     tmp.append(col.name)
                 self.colnames = tuple(tmp)
-                self.columns = columns
+                self.columns = tuple(columns)
         else:
             # Calculate the order of column names
             if columns is None:
@@ -304,7 +306,7 @@ def __init__(self, **kwargs):  # noqa: C901
                         pos = order[col.target.name]
                         tmp[pos] = col
                         tmp[pos+1] = col.target
-                self.columns = list(tmp)
+                self.columns = tuple(tmp)
 
         # to make generating DataFrames and Series easier
         col_dict = dict()

tests/unit/common/test_table.py

@@ -37,9 +37,10 @@ def with_spec(self):
         return table
 
     def check_empty_table(self, table):
+        self.assertIsInstance(table.columns, tuple)
         self.assertIsInstance(table.columns[0], VectorData)
         self.assertEqual(len(table.columns), 3)
-        self.assertEqual(table.colnames, ('foo', 'bar', 'baz'))
+        self.assertTupleEqual(table.colnames, ('foo', 'bar', 'baz'))
 
     def test_constructor_table_columns(self):
         table = self.with_table_columns()
@@ -134,7 +135,7 @@ def test_get_item(self):
     def test_add_column(self):
         table = self.with_spec()
         table.add_column(name='qux', description='qux column')
-        self.assertEqual(table.colnames, ('foo', 'bar', 'baz', 'qux'))
+        self.assertTupleEqual(table.colnames, ('foo', 'bar', 'baz', 'qux'))
         self.assertTrue(hasattr(table, 'qux'))
 
     def test_add_column_twice(self):
@@ -403,6 +404,11 @@ def test_init_columns_existing_attr(self):
                 with self.assertWarnsWith(UserWarning, msg):
                     DynamicTable("test_table", 'a test table', columns=cols)
 
+    def test_colnames_none(self):
+        table = DynamicTable('table0', 'an example table')
+        self.assertTupleEqual(table.colnames, tuple())
+        self.assertTupleEqual(table.columns, tuple())
+
 
 class TestDynamicTableRoundTrip(H5RoundTripMixin, TestCase):
 
@@ -417,6 +423,14 @@ def setUpContainer(self):
         return table
 
 
+class TestEmptyDynamicTableRoundTrip(H5RoundTripMixin, TestCase):
+    """Test roundtripping a DynamicTable with no rows and no columns."""
+
+    def setUpContainer(self):
+        table = DynamicTable('table0', 'an example table')
+        return table
+
+
 class TestDynamicTableRegion(TestCase):
 
     def setUp(self):