Raise HeadersNeeded instead of TypeError when subscripting a headerless Dataset by column name (#648)

Author: gaoflow

src/tablib/core.py

@@ -176,6 +176,8 @@ def __len__(self):
 
     def __getitem__(self, key):
         if isinstance(key, str):
+            if self.headers is None:
+                raise HeadersNeeded()
             if key in self.headers:
                 pos = self.headers.index(key)  # get 'key' index from each data
                 return [row[pos] for row in self._data]
@@ -194,6 +196,8 @@ def __setitem__(self, key, value):
 
     def __delitem__(self, key):
         if isinstance(key, str):
+            if self.headers is None:
+                raise HeadersNeeded()
 
             if key in self.headers:
 

tests/test_tablib.py

@@ -322,6 +322,20 @@ def test_delete(self):
         # Delete from invalid index
         self.assertRaises(IndexError, self.founders.__delitem__, 3)
 
+    def test_getitem_str_key_no_headers_raises(self):
+        """Verify that accessing by column name on a headerless Dataset raises HeadersNeeded."""
+        d = tablib.Dataset()
+        d.append([1, 2, 3])
+        with self.assertRaises(tablib.core.HeadersNeeded):
+            _ = d['col']
+
+    def test_delitem_str_key_no_headers_raises(self):
+        """Verify that deleting by column name on a headerless Dataset raises HeadersNeeded."""
+        d = tablib.Dataset()
+        d.append([1, 2, 3])
+        with self.assertRaises(tablib.core.HeadersNeeded):
+            del d['col']
+
     def test_str_no_columns(self):
         d = tablib.Dataset(['a', 1], ['b', 2], ['c', 3])
         output = f'{d}'