Inheritance of bags and better jupyter output for pretty printer.

tests/features/test_inherit.py

@@ -0,0 +1,27 @@
+from bonobo.constants import INHERIT
+from bonobo.util.testing import BufferingNodeExecutionContext
+
+messages = [
+    ('Hello', ),
+    ('Goodbye', ),
+]
+
+
+def append(*args):
+    return INHERIT, '!'
+
+
+def test_inherit():
+    with BufferingNodeExecutionContext(append) as context:
+        context.write_sync(*messages)
+
+    assert context.get_buffer() == list(map(lambda x: x + ('!', ), messages))
+
+
+def test_inherit_bag_tuple():
+    with BufferingNodeExecutionContext(append) as context:
+        context.set_input_fields(['message'])
+        context.write_sync(*messages)
+
+    assert context.get_output_fields() == ('message', '0')
+    assert context.get_buffer() == list(map(lambda x: x + ('!', ), messages))