No longer using stderr and self.data together to determine truthiness of a CommandResult.

Either self.data is used or if that's not possible, then self.stderr is used.
This provided applications the ability to print to stderr even if an error didn't occur.

2 files changed, 25 insertions, 4 deletions

diff --git a/cmd2/pyscript_bridge.py b/cmd2/pyscript_bridge.py
index 2002ca6d..dcfd9116 100644
--- a/cmd2/pyscript_bridge.py
+++ b/cmd2/pyscript_bridge.py
@@ -33,9 +33,16 @@ class CommandResult(namedtuple_with_defaults('CommandResult', ['stdout', 'stderr
 
     NOTE: Named tuples are immutable.  So the contents are there for access, not for modification.
     """
-    def __bool__(self):
-        """If stderr is None and data is not None the command is considered a success"""
-        return not self.stderr and self.data is not None
+    def __bool__(self) -> bool:
+        """Returns True if the command succeeded, otherwise False"""
+
+        # If data has a __bool__ method, then call it to determine success of command
+        if self.data is not None and callable(getattr(self.data, '__bool__', None)):
+            return True if self.data else False
+
+        # Otherwise check if stderr was filled out
+        else:
+            return not self.stderr
 
 
 def _exec_cmd(cmd2_app, func: Callable, echo: bool) -> CommandResult:
diff --git a/tests/test_cmd2.py b/tests/test_cmd2.py
index a64f21e4..a2bd6197 100644
--- a/tests/test_cmd2.py
+++ b/tests/test_cmd2.py
@@ -1576,8 +1576,14 @@ class CommandResultApp(cmd2.Cmd):
         self._last_result = cmd2.CommandResult(arg, data=True)
 
     def do_negative(self, arg):
+        self._last_result = cmd2.CommandResult(arg, data=False)
+
+    def do_affirmative_no_data(self, arg):
         self._last_result = cmd2.CommandResult(arg)
 
+    def do_negative_no_data(self, arg):
+        self._last_result = cmd2.CommandResult('', arg)
+
 @pytest.fixture
 def commandresult_app():
     app = CommandResultApp()
@@ -1590,11 +1596,19 @@ def test_commandresult_truthy(commandresult_app):
     assert commandresult_app._last_result
     assert commandresult_app._last_result == cmd2.CommandResult(arg, data=True)
 
+    run_cmd(commandresult_app, 'affirmative_no_data {}'.format(arg))
+    assert commandresult_app._last_result
+    assert commandresult_app._last_result == cmd2.CommandResult(arg)
+
 def test_commandresult_falsy(commandresult_app):
     arg = 'bar'
     run_cmd(commandresult_app, 'negative {}'.format(arg))
     assert not commandresult_app._last_result
-    assert commandresult_app._last_result == cmd2.CommandResult(arg)
+    assert commandresult_app._last_result == cmd2.CommandResult(arg, data=False)
+
+    run_cmd(commandresult_app, 'negative_no_data {}'.format(arg))
+    assert not commandresult_app._last_result
+    assert commandresult_app._last_result == cmd2.CommandResult('', arg)
 
 
 def test_is_text_file_bad_input(base_app):