Merge pull request #727 from oliver-sanders/722

Author: blink1073

docs/source/changelog.rst

@@ -4,6 +4,12 @@ Changes in Traitlets
 Traitlets 5.2
 -------------
 
+5.2.1
+*****
+
+  - logging: Don't attempt to close handlers unless they have been opened.
+    Fixes ``ValueError: Unable to configure formatter 'console'`` traceback.
+
 5.2.0
 *****
 

traitlets/config/application.py

@@ -276,6 +276,8 @@ def _configure_logging(self):
         config = self.get_default_logging_config()
         nested_update(config, self.logging_config or {})
         dictConfig(config)
+        # make a note that we have configured logging
+        self._logging_configured = True
 
     @default("log")
     def _log_default(self):
@@ -942,9 +944,14 @@ def generate_config_file(self, classes=None):
         return "\n".join(lines)
 
     def close_handlers(self):
-        for handler in self.log.handlers:
-            with suppress(Exception):
-                handler.close()
+        if getattr(self, "_logging_configured", False):
+            # don't attempt to close handlers unless they have been opened
+            # (note accessing self.log.handlers will create handlers if they
+            # have not yet been initialised)
+            for handler in self.log.handlers:
+                with suppress(Exception):
+                    handler.close()
+            self._logging_configured = False
 
     def exit(self, exit_status=0):
         self.log.debug("Exiting application: %s" % self.name)

traitlets/config/tests/test_application.py

@@ -804,6 +804,50 @@ def test_logging_config(tmp_path, capsys):
     assert capsys.readouterr().err == "[Application] WARNING | warn\n"
 
 
+@pytest.fixture
+def caplogconfig(monkeypatch):
+    """Capture logging config events for DictConfigurator objects.
+
+    This suppresses the event (so the configuration doesn't happen).
+
+    Returns a list of (args, kwargs).
+    """
+    calls = []
+
+    def _configure(*args, **kwargs):
+        nonlocal calls
+        calls.append((args, kwargs))
+
+    monkeypatch.setattr(
+        "logging.config.DictConfigurator.configure",
+        _configure,
+    )
+
+    return calls
+
+
+def test_logging_teardown_on_error(capsys, caplogconfig):
+    """Ensure we don't try to open logs in order to close them (See #722).
+
+    If you try to configure logging handlers whilst Python is shutting down
+    you may get traceback.
+    """
+    # create and destroy an app (without configuring logging)
+    # (ensure that the logs were not configured)
+    app = Application()
+    del app
+    assert len(caplogconfig) == 0  # logging was not configured
+    out, err = capsys.readouterr()
+    assert "Traceback" not in err
+
+    # ensure that the logs would have been configured otherwise
+    # (to prevent this test from yielding false-negatives)
+    app = Application()
+    app._logging_configured = True  # make it look like logging was configured
+    del app
+    assert len(caplogconfig) == 1  # logging was configured
+
+
 if __name__ == "__main__":
     # for test_help_output:
     MyApp.launch_instance()