Render empty robust tables without raising ValueError

humanfriendly/tables.py

@@ -261,7 +261,7 @@ def format_robust_table(data, column_names):
         blocks.append(lines)
     # Calculate the width of the row delimiter.
     num_rows, num_columns = find_terminal_size()
-    longest_line = max(max(map(ansi_width, lines)) for lines in blocks)
+    longest_line = max([ansi_width(line) for lines in blocks for line in lines] or [0])
     delimiter = u"\n%s\n" % ('-' * min(longest_line, num_columns))
     # Force a delimiter at the start and end of the table.
     blocks.insert(0, "")

humanfriendly/tests.py

@@ -130,6 +130,13 @@ class HumanFriendlyTestCase(TestCase):
 
     """Container for the `humanfriendly` test suite."""
 
+    def test_empty_robust_table(self):
+        """Empty query results produce no rows instead of raising ValueError."""
+        from humanfriendly.tables import format_robust_table
+        assert format_robust_table([], ['name', 'value']) == ''
+        assert format_robust_table(iter([]), ['name']) == ''
+        assert format_robust_table([[]], []) == ''
+
     def test_case_insensitive_dict(self):
         """Test the CaseInsensitiveDict class."""
         # Test support for the dict(iterable) signature.