Skip members that raise when listing them for help

fire/completion.py

@@ -359,7 +359,7 @@ def VisibleMembers(component, class_attrs=None, verbose=False):
   if isinstance(component, dict):
     members = component.items()
   else:
-    members = inspect.getmembers(component)
+    members = inspectutils.GetMembers(component)
 
   # If class_attrs has not been provided, compute it.
   if class_attrs is None:

fire/core.py

@@ -225,7 +225,7 @@ def _IsHelpShortcut(component_trace, remaining_args):
         _, remaining_kwargs, _ = _ParseKeywordArgs(remaining_args, fn_spec)
         show_help = target in remaining_kwargs
       else:
-        members = dict(inspect.getmembers(component))
+        members = dict(inspectutils.GetMembers(component))
         show_help = target not in members
 
   if show_help:

fire/fire_test.py

@@ -556,6 +556,35 @@ def testHelpFlagAndTraceFlag(self):
     with self.assertRaisesFireExit(0, 'Fire trace:\n.*SYNOPSIS'):
       fire.Fire(tc.BoolConverter, command=['--', '-h', '--trace'])
 
+  def testHelpWithRaisingProperty(self):
+    # A property whose getter raises should not prevent help from being shown.
+    # See https://github.com/google/python-fire/issues/672.
+    class Component(object):
+
+      @property
+      def broken(self):
+        raise RuntimeError('backend unavailable')
+
+      def works(self, value):
+        return value
+
+    component = Component()
+
+    # Bare invocation prints the component's help without crashing.
+    with self.assertOutputMatches(stdout='.*works.*'):
+      result = fire.Fire(component, command=[])
+    self.assertEqual(result, component)
+
+    # Both the --help flag and the --help shortcut list the working command.
+    with self.assertRaisesFireExit(0, 'works'):
+      fire.Fire(component, command=['--', '--help'])
+    with self.assertRaisesFireExit(0, 'works'):
+      fire.Fire(component, command=['--help'])
+
+    # The broken property is still usable directly, but raises on access.
+    with self.assertRaises(RuntimeError):
+      component.broken  # pylint: disable=pointless-statement
+
   def testTabCompletionNoName(self):
     completion_script = fire.Fire(tc.NoDefaults, command=['--', '--completion'])
     self.assertIn('double', completion_script)

fire/inspectutils.py

@@ -342,6 +342,33 @@ def GetClassAttrsDict(component):
   }
 
 
+def GetMembers(component):
+  """Returns a list of (name, member) pairs for the members of component.
+
+  Reading a member can run arbitrary code, such as a property getter, which may
+  raise an exception. inspect.getmembers aborts on any exception that is not an
+  AttributeError, which would crash Fire while it only intends to enumerate the
+  members of the component, for example to build help text. This falls back to
+  reading the members one at a time and skipping any that cannot be read, so a
+  single broken member does not prevent the rest from being listed.
+
+  Args:
+    component: The object whose members to list.
+  Returns:
+    A list of (name, value) pairs for the readable members of component.
+  """
+  try:
+    return inspect.getmembers(component)
+  except Exception:  # pylint: disable=broad-except
+    members = []
+    for name in dir(component):
+      try:
+        members.append((name, getattr(component, name)))
+      except Exception:  # pylint: disable=broad-except
+        continue
+    return members
+
+
 def IsCoroutineFunction(fn):
   try:
     return inspect.iscoroutinefunction(fn)