Use package name when __main__.py is used

fire/core.py

@@ -103,7 +103,14 @@ def Fire(component=None, command=None, name=None, serialize=None):
         code 2. When used with the help or trace flags, Fire will raise a
         FireExit with code 0 if successful.
   """
-  name = name or os.path.basename(sys.argv[0])
+  if not name:
+    script_name = sys.argv[0]
+    if os.path.basename(script_name) == '__main__.py':
+      # If invoked via `python -m package`, use the package name rather than
+      # the generic `__main__.py` filename.
+      name = os.path.basename(os.path.dirname(os.path.abspath(script_name)))
+    else:
+      name = os.path.basename(script_name)
 
   # Get args as a list.
   if isinstance(command, str):

fire/fire_test.py

@@ -57,6 +57,17 @@ def testFireDefaultName(self):
                                     stderr=None):
         fire.Fire(tc.Empty)
 
+  def testFireDefaultNameDunderMain(self):
+    # When invoked as `python -m package`, sys.argv[0] is the path to the
+    # package's __main__.py file. The package name should be used instead of
+    # `__main__.py` in the usage output.
+    with mock.patch.object(sys, 'argv',
+                           [os.path.join('python-fire', 'fire', 'mypackage',
+                                         '__main__.py')]):
+      with self.assertOutputMatches(stdout='SYNOPSIS.*mypackage',
+                                    stderr=None):
+        fire.Fire(tc.Empty)
+
   def testFireNoArgs(self):
     self.assertEqual(fire.Fire(tc.MixedDefaults, command=['ten']), 10)