fix(text): don't crash on --query lists mixing scalars and objects

.changes/next-release/bugfix-text-output-mixed-list.json

@@ -0,0 +1,5 @@
+{
+  "category": "``text`` output",
+  "description": "Fix ``AttributeError`` when ``--output text`` renders a list that contains both a scalar and an object, which a ``--query`` multi-select list such as ``[InstanceId, State]`` produces",
+  "type": "bugfix"
+}

awscli/text.py

@@ -85,6 +85,11 @@ def _format_dict(scalar_keys, item, identifier, stream):
 def _all_scalar_keys(list_of_dicts):
     keys_seen = set()
     for item_dict in list_of_dicts:
+        if not isinstance(item_dict, dict):
+            # The list is only required to contain *at least* one dict,
+            # so skip over any elements that aren't dicts.  They are
+            # rendered on their own by _format_text.
+            continue
         for key, value in item_dict.items():
             if not isinstance(value, (dict, list)):
                 keys_seen.add(key)

tests/unit/test_text.py

@@ -219,6 +219,22 @@ def test_deeply_nested_with_identifier(self):
             'FOO\th\n'
         )
 
+    def test_dicts_mixed_with_scalars(self):
+        # A --query multi-select list such as '[InstanceId, State]'
+        # produces a list holding both a scalar and a dict.
+        self.assert_text_renders_to(
+            ['i-123', dict(Code=16, Name='running')],
+            'i-123\n'
+            '16\trunning\n'
+        )
+
+    def test_dicts_mixed_with_lists(self):
+        self.assert_text_renders_to(
+            [['a', 'b'], dict(Code=16, Name='running')],
+            'a\tb\n'
+            '16\trunning\n'
+        )
+
 
 if __name__ == '__main__':
     unittest.main()