[3.7] bpo-36492: Fix passing special keyword arguments to some functions. (GH-12637) (GH-12645)

The following arguments can be passed as keyword arguments for passing
to other function if the corresponding required argument is passed as
positional:

- "func" in functools.partialmethod(), weakref.finalize(),
  profile.Profile.runcall(), cProfile.Profile.runcall(),
  bdb.Bdb.runcall(), trace.Trace.runfunc() and
  curses.wrapper().
- "function" in unittest.addModuleCleanup() and
  unittest.TestCase.addCleanup().
- "fn" in the submit() method of concurrent.futures.ThreadPoolExecutor
  and concurrent.futures.ProcessPoolExecutor.
- "callback" in contextlib.ExitStack.callback(),
  contextlib.AsyncExitStack.callback() and
  contextlib.AsyncExitStack.push_async_callback().
- "c" and "typeid" in multiprocessing.managers.Server.create().
- "obj" in weakref.finalize().

(cherry picked from commit 42a139ed88c487f325a241c6ee8b308b3c045975)

20 files changed, 282 insertions, 17 deletions

diff --git a/Lib/bdb.py b/Lib/bdb.py
index 25c6260c47..caf207733b 100644
--- a/Lib/bdb.py
+++ b/Lib/bdb.py
@@ -616,11 +616,23 @@ class Bdb:
 
     # This method is more useful to debug a single function call.
 
-    def runcall(self, func, *args, **kwds):
+    def runcall(*args, **kwds):
         """Debug a single function call.
 
         Return the result of the function call.
         """
+        if len(args) >= 2:
+            self, func, *args = args
+        elif not args:
+            raise TypeError("descriptor 'runcall' of 'Bdb' object "
+                            "needs an argument")
+        elif 'func' in kwds:
+            func = kwds.pop('func')
+            self, *args = args
+        else:
+            raise TypeError('runcall expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         self.reset()
         sys.settrace(self.trace_dispatch)
         res = None
diff --git a/Lib/cProfile.py b/Lib/cProfile.py
index f6e423b3dd..9485d3d515 100755
--- a/Lib/cProfile.py
+++ b/Lib/cProfile.py
@@ -103,7 +103,19 @@ class Profile(_lsprof.Profiler):
         return self
 
     # This method is more useful to profile a single function call.
-    def runcall(self, func, *args, **kw):
+    def runcall(*args, **kw):
+        if len(args) >= 2:
+            self, func, *args = args
+        elif not args:
+            raise TypeError("descriptor 'runcall' of 'Profile' object "
+                            "needs an argument")
+        elif 'func' in kw:
+            func = kw.pop('func')
+            self, *args = args
+        else:
+            raise TypeError('runcall expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         self.enable()
         try:
             return func(*args, **kw)
diff --git a/Lib/concurrent/futures/_base.py b/Lib/concurrent/futures/_base.py
index 61c81bb7fe..0b847307a3 100644
--- a/Lib/concurrent/futures/_base.py
+++ b/Lib/concurrent/futures/_base.py
@@ -536,7 +536,7 @@ class Future(object):
 class Executor(object):
     """This is an abstract base class for concrete asynchronous executors."""
 
-    def submit(self, fn, *args, **kwargs):
+    def submit(*args, **kwargs):
         """Submits a callable to be executed with the given arguments.
 
         Schedules the callable to be executed as fn(*args, **kwargs) and returns
@@ -545,6 +545,15 @@ class Executor(object):
         Returns:
             A Future representing the given call.
         """
+        if len(args) >= 2:
+            pass
+        elif not args:
+            raise TypeError("descriptor 'submit' of 'Executor' object "
+                            "needs an argument")
+        elif 'fn' not in kwargs:
+            raise TypeError('submit expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         raise NotImplementedError()
 
     def map(self, fn, *iterables, timeout=None, chunksize=1):
diff --git a/Lib/concurrent/futures/process.py b/Lib/concurrent/futures/process.py
index ce7d642b09..8a0ed98b3e 100644
--- a/Lib/concurrent/futures/process.py
+++ b/Lib/concurrent/futures/process.py
@@ -593,7 +593,19 @@ class ProcessPoolExecutor(_base.Executor):
             p.start()
             self._processes[p.pid] = p
 
-    def submit(self, fn, *args, **kwargs):
+    def submit(*args, **kwargs):
+        if len(args) >= 2:
+            self, fn, *args = args
+        elif not args:
+            raise TypeError("descriptor 'submit' of 'ProcessPoolExecutor' object "
+                            "needs an argument")
+        elif 'fn' in kwargs:
+            fn = kwargs.pop('fn')
+            self, *args = args
+        else:
+            raise TypeError('submit expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         with self._shutdown_lock:
             if self._broken:
                 raise BrokenProcessPool(self._broken)
diff --git a/Lib/concurrent/futures/thread.py b/Lib/concurrent/futures/thread.py
index 78359711d5..c7c9ef44c6 100644
--- a/Lib/concurrent/futures/thread.py
+++ b/Lib/concurrent/futures/thread.py
@@ -142,7 +142,19 @@ class ThreadPoolExecutor(_base.Executor):
         self._initializer = initializer
         self._initargs = initargs
 
-    def submit(self, fn, *args, **kwargs):
+    def submit(*args, **kwargs):
+        if len(args) >= 2:
+            self, fn, *args = args
+        elif not args:
+            raise TypeError("descriptor 'submit' of 'ThreadPoolExecutor' object "
+                            "needs an argument")
+        elif 'fn' in kwargs:
+            fn = kwargs.pop('fn')
+            self, *args = args
+        else:
+            raise TypeError('submit expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         with self._shutdown_lock:
             if self._broken:
                 raise BrokenThreadPool(self._broken)
diff --git a/Lib/contextlib.py b/Lib/contextlib.py
index 1ff8cdf1ce..2d745ea3e3 100644
--- a/Lib/contextlib.py
+++ b/Lib/contextlib.py
@@ -378,7 +378,8 @@ class _BaseExitStack:
         return _exit_wrapper
 
     @staticmethod
-    def _create_cb_wrapper(callback, *args, **kwds):
+    def _create_cb_wrapper(*args, **kwds):
+        callback, *args = args
         def _exit_wrapper(exc_type, exc, tb):
             callback(*args, **kwds)
         return _exit_wrapper
@@ -427,11 +428,23 @@ class _BaseExitStack:
         self._push_cm_exit(cm, _exit)
         return result
 
-    def callback(self, callback, *args, **kwds):
+    def callback(*args, **kwds):
         """Registers an arbitrary callback and arguments.
 
         Cannot suppress exceptions.
         """
+        if len(args) >= 2:
+            self, callback, *args = args
+        elif not args:
+            raise TypeError("descriptor 'callback' of '_BaseExitStack' object "
+                            "needs an argument")
+        elif 'callback' in kwds:
+            callback = kwds.pop('callback')
+            self, *args = args
+        else:
+            raise TypeError('callback expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         _exit_wrapper = self._create_cb_wrapper(callback, *args, **kwds)
 
         # We changed the signature, so using @wraps is not appropriate, but
@@ -540,7 +553,8 @@ class AsyncExitStack(_BaseExitStack, AbstractAsyncContextManager):
         return _exit_wrapper
 
     @staticmethod
-    def _create_async_cb_wrapper(callback, *args, **kwds):
+    def _create_async_cb_wrapper(*args, **kwds):
+        callback, *args = args
         async def _exit_wrapper(exc_type, exc, tb):
             await callback(*args, **kwds)
         return _exit_wrapper
@@ -575,11 +589,23 @@ class AsyncExitStack(_BaseExitStack, AbstractAsyncContextManager):
             self._push_async_cm_exit(exit, exit_method)
         return exit  # Allow use as a decorator
 
-    def push_async_callback(self, callback, *args, **kwds):
+    def push_async_callback(*args, **kwds):
         """Registers an arbitrary coroutine function and arguments.
 
         Cannot suppress exceptions.
         """
+        if len(args) >= 2:
+            self, callback, *args = args
+        elif not args:
+            raise TypeError("descriptor 'push_async_callback' of "
+                            "'AsyncExitStack' object needs an argument")
+        elif 'callback' in kwds:
+            callback = kwds.pop('callback')
+            self, *args = args
+        else:
+            raise TypeError('push_async_callback expected at least 1 '
+                            'positional argument, got %d' % (len(args)-1))
+
         _exit_wrapper = self._create_async_cb_wrapper(callback, *args, **kwds)
 
         # We changed the signature, so using @wraps is not appropriate, but
diff --git a/Lib/curses/__init__.py b/Lib/curses/__init__.py
index 47378741ac..b3373af70e 100644
--- a/Lib/curses/__init__.py
+++ b/Lib/curses/__init__.py
@@ -60,7 +60,7 @@ except NameError:
 # raises an exception, wrapper() will restore the terminal to a sane state so
 # you can read the resulting traceback.
 
-def wrapper(func, *args, **kwds):
+def wrapper(*args, **kwds):
     """Wrapper function that initializes curses and calls another function,
     restoring normal keyboard/screen behavior on error.
     The callable object 'func' is then passed the main window 'stdscr'
@@ -68,6 +68,14 @@ def wrapper(func, *args, **kwds):
     wrapper().
     """
 
+    if args:
+        func, *args = args
+    elif 'func' in kwds:
+        func = kwds.pop('func')
+    else:
+        raise TypeError('wrapper expected at least 1 positional argument, '
+                        'got %d' % len(args))
+
     try:
         # Initialize curses
         stdscr = initscr()
diff --git a/Lib/functools.py b/Lib/functools.py
index b734899b56..1daa1d1775 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -323,7 +323,20 @@ class partialmethod(object):
     callables as instance methods.
     """
 
-    def __init__(self, func, *args, **keywords):
+    def __init__(*args, **keywords):
+        if len(args) >= 2:
+            self, func, *args = args
+        elif not args:
+            raise TypeError("descriptor '__init__' of partialmethod "
+                            "needs an argument")
+        elif 'func' in keywords:
+            func = keywords.pop('func')
+            self, *args = args
+        else:
+            raise TypeError("type 'partialmethod' takes at least one argument, "
+                            "got %d" % (len(args)-1))
+        args = tuple(args)
+
         if not callable(func) and not hasattr(func, "__get__"):
             raise TypeError("{!r} is not callable or a descriptor"
                                  .format(func))
diff --git a/Lib/multiprocessing/managers.py b/Lib/multiprocessing/managers.py
index 4ae8ddc770..8e8d28f4b7 100644
--- a/Lib/multiprocessing/managers.py
+++ b/Lib/multiprocessing/managers.py
@@ -351,10 +351,30 @@ class Server(object):
         finally:
             self.stop_event.set()
 
-    def create(self, c, typeid, *args, **kwds):
+    def create(*args, **kwds):
         '''
         Create a new shared object and return its id
         '''
+        if len(args) >= 3:
+            self, c, typeid, *args = args
+        elif not args:
+            raise TypeError("descriptor 'create' of 'Server' object "
+                            "needs an argument")
+        else:
+            if 'typeid' not in kwds:
+                raise TypeError('create expected at least 2 positional '
+                                'arguments, got %d' % (len(args)-1))
+            typeid = kwds.pop('typeid')
+            if len(args) >= 2:
+                self, c, *args = args
+            else:
+                if 'c' not in kwds:
+                    raise TypeError('create expected at least 2 positional '
+                                    'arguments, got %d' % (len(args)-1))
+                c = kwds.pop('c')
+                self, *args = args
+        args = tuple(args)
+
         with self.mutex:
             callable, exposed, method_to_typeid, proxytype = \
                       self.registry[typeid]
@@ -576,10 +596,13 @@ class BaseManager(object):
         util.info('manager serving at %r', server.address)
         server.serve_forever()
 
-    def _create(self, typeid, *args, **kwds):
+    def _create(*args, **kwds):
         '''
         Create a new shared object; return the token and exposed tuple
         '''
+        self, typeid, *args = args
+        args = tuple(args)
+
         assert self._state.value == State.STARTED, 'server not yet started'
         conn = self._Client(self._address, authkey=self._authkey)
         try:
diff --git a/Lib/profile.py b/Lib/profile.py
index 0340a7907b..c26f0c8bfa 100755
--- a/Lib/profile.py
+++ b/Lib/profile.py
@@ -425,7 +425,19 @@ class Profile:
         return self
 
     # This method is more useful to profile a single function call.
-    def runcall(self, func, *args, **kw):
+    def runcall(*args, **kw):
+        if len(args) >= 2:
+            self, func, *args = args
+        elif not args:
+            raise TypeError("descriptor 'runcall' of 'Profile' object "
+                            "needs an argument")
+        elif 'func' in kw:
+            func = kw.pop('func')
+            self, *args = args
+        else:
+            raise TypeError('runcall expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         self.set_cmd(repr(func))
         sys.setprofile(self.dispatcher)
         try:
diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py
index 7e5a4edf80..59aa0f46f5 100644
--- a/Lib/test/test_concurrent_futures.py
+++ b/Lib/test/test_concurrent_futures.py
@@ -49,6 +49,9 @@ INITIALIZER_STATUS = 'uninitialized'
 def mul(x, y):
     return x * y
 
+def capture(*args, **kwargs):
+    return args, kwargs
+
 def sleep_and_raise(t):
     time.sleep(t)
     raise Exception('this is an exception')
@@ -658,6 +661,12 @@ class ExecutorTest:
     def test_submit_keyword(self):
         future = self.executor.submit(mul, 2, y=8)
         self.assertEqual(16, future.result())
+        future = self.executor.submit(capture, 1, self=2, fn=3)
+        self.assertEqual(future.result(), ((1,), {'self': 2, 'fn': 3}))
+        future = self.executor.submit(fn=capture, arg=1)
+        self.assertEqual(future.result(), ((), {'arg': 1}))
+        with self.assertRaises(TypeError):
+            self.executor.submit(arg=1)
 
     def test_map(self):
         self.assertEqual(
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 2a44404a60..30c2e27b3c 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -575,6 +575,7 @@ class TestBaseExitStack:
             ((), dict(example=1)),
             ((1,), dict(example=1)),
             ((1,2), dict(example=1)),
+            ((1,2), dict(self=3, callback=4)),
         ]
         result = []
         def _exit(*args, **kwds):
@@ -597,6 +598,15 @@ class TestBaseExitStack:
                 self.assertIsNone(wrapper[1].__doc__, _exit.__doc__)
         self.assertEqual(result, expected)
 
+        result = []
+        with self.exit_stack() as stack:
+            with self.assertRaises(TypeError):
+                stack.callback(arg=1)
+            with self.assertRaises(TypeError):
+                self.exit_stack.callback(arg=2)
+            stack.callback(callback=_exit, arg=3)
+        self.assertEqual(result, [((), {'arg': 3})])
+
     def test_push(self):
         exc_raised = ZeroDivisionError
         def _expect_exc(exc_type, exc, exc_tb):
diff --git a/Lib/test/test_contextlib_async.py b/Lib/test/test_contextlib_async.py
index e34fc38d11..cc38dcf8c4 100644
--- a/Lib/test/test_contextlib_async.py
+++ b/Lib/test/test_contextlib_async.py
@@ -329,6 +329,15 @@ class TestAsyncExitStack(TestBaseExitStack, unittest.TestCase):
 
         self.assertEqual(result, expected)
 
+        result = []
+        async with AsyncExitStack() as stack:
+            with self.assertRaises(TypeError):
+                stack.push_async_callback(arg=1)
+            with self.assertRaises(TypeError):
+                self.exit_stack.push_async_callback(arg=2)
+            stack.push_async_callback(callback=_exit, arg=3)
+        self.assertEqual(result, [((), {'arg': 3})])
+
     @_async_test
     async def test_async_push(self):
         exc_raised = ZeroDivisionError
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index a91c6348e7..a7625d6090 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -464,6 +464,7 @@ class TestPartialMethod(unittest.TestCase):
         positional = functools.partialmethod(capture, 1)
         keywords = functools.partialmethod(capture, a=2)
         both = functools.partialmethod(capture, 3, b=4)
+        spec_keywords = functools.partialmethod(capture, self=1, func=2)
 
         nested = functools.partialmethod(positional, 5)
 
@@ -497,6 +498,8 @@ class TestPartialMethod(unittest.TestCase):
 
         self.assertEqual(self.A.both(self.a, 5, c=6), ((self.a, 3, 5), {'b': 4, 'c': 6}))
 
+        self.assertEqual(self.a.spec_keywords(), ((self.a,), {'self': 1, 'func': 2}))
+
     def test_nested(self):
         self.assertEqual(self.a.nested(), ((self.a, 1, 5), {}))
         self.assertEqual(self.a.nested(6), ((self.a, 1, 5, 6), {}))
@@ -550,6 +553,13 @@ class TestPartialMethod(unittest.TestCase):
         with self.assertRaises(TypeError):
             class B(object):
                 method = functools.partialmethod(None, 1)
+        with self.assertRaises(TypeError):
+            class B:
+                method = functools.partialmethod()
+        class B:
+            method = functools.partialmethod(func=capture, a=1)
+        b = B()
+        self.assertEqual(b.method(2, x=3), ((b, 2), {'a': 1, 'x': 3}))
 
     def test_repr(self):
         self.assertEqual(repr(vars(self.A)['both']),
diff --git a/Lib/test/test_trace.py b/Lib/test/test_trace.py
index 63f474179d..66fff1cef4 100644
--- a/Lib/test/test_trace.py
+++ b/Lib/test/test_trace.py
@@ -70,6 +70,9 @@ def traced_func_calling_generator():
 def traced_doubler(num):
     return num * 2
 
+def traced_capturer(*args, **kwargs):
+    return args, kwargs
+
 def traced_caller_list_comprehension():
     k = 10
     mylist = [traced_doubler(i) for i in range(k)]
@@ -238,6 +241,14 @@ class TestFuncs(unittest.TestCase):
         }
         self.assertEqual(self.tracer.results().calledfuncs, expected)
 
+    def test_arg_errors(self):
+        res = self.tracer.runfunc(traced_capturer, 1, 2, self=3, func=4)
+        self.assertEqual(res, ((1, 2), {'self': 3, 'func': 4}))
+        res = self.tracer.runfunc(func=traced_capturer, arg=1)
+        self.assertEqual(res, ((), {'arg': 1}))
+        with self.assertRaises(TypeError):
+            self.tracer.runfunc()
+
     def test_loop_caller_importing(self):
         self.tracer.runfunc(traced_func_importing_caller, 1)
 
diff --git a/Lib/test/test_weakref.py b/Lib/test/test_weakref.py
index 1fac08dafc..ad7a6acfcc 100644
--- a/Lib/test/test_weakref.py
+++ b/Lib/test/test_weakref.py
@@ -1839,6 +1839,33 @@ class FinalizeTestCase(unittest.TestCase):
         self.assertEqual(f.alive, False)
         self.assertEqual(res, [199])
 
+    def test_arg_errors(self):
+        def fin(*args, **kwargs):
+            res.append((args, kwargs))
+
+        a = self.A()
+
+        res = []
+        f = weakref.finalize(a, fin, 1, 2, func=3, obj=4)
+        self.assertEqual(f.peek(), (a, fin, (1, 2), {'func': 3, 'obj': 4}))
+        f()
+        self.assertEqual(res, [((1, 2), {'func': 3, 'obj': 4})])
+
+        res = []
+        f = weakref.finalize(a, func=fin, arg=1)
+        self.assertEqual(f.peek(), (a, fin, (), {'arg': 1}))
+        f()
+        self.assertEqual(res, [((), {'arg': 1})])
+
+        res = []
+        f = weakref.finalize(obj=a, func=fin, arg=1)
+        self.assertEqual(f.peek(), (a, fin, (), {'arg': 1}))
+        f()
+        self.assertEqual(res, [((), {'arg': 1})])
+
+        self.assertRaises(TypeError, weakref.finalize, a)
+        self.assertRaises(TypeError, weakref.finalize)
+
     def test_order(self):
         a = self.A()
         res = []
diff --git a/Lib/trace.py b/Lib/trace.py
index 0ed7ba95b5..206bd2b689 100755
--- a/Lib/trace.py
+++ b/Lib/trace.py
@@ -452,7 +452,19 @@ class Trace:
                 sys.settrace(None)
                 threading.settrace(None)
 
-    def runfunc(self, func, *args, **kw):
+    def runfunc(*args, **kw):
+        if len(args) >= 2:
+            self, func, *args = args
+        elif not args:
+            raise TypeError("descriptor 'runfunc' of 'Trace' object "
+                            "needs an argument")
+        elif 'func' in kw:
+            func = kw.pop('func')
+            self, *args = args
+        else:
+            raise TypeError('runfunc expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         result = None
         if not self.donothing:
             sys.settrace(self.globaltrace)
diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index 758924d801..811f5df23d 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -442,12 +442,25 @@ class TestCase(object):
         """
         self._type_equality_funcs[typeobj] = function
 
-    def addCleanup(self, function, *args, **kwargs):
+    def addCleanup(*args, **kwargs):
         """Add a function, with arguments, to be called when the test is
         completed. Functions added are called on a LIFO basis and are
         called after tearDown on test failure or success.
 
         Cleanup items are called even if setUp fails (unlike tearDown)."""
+        if len(args) >= 2:
+            self, function, *args = args
+        elif not args:
+            raise TypeError("descriptor 'addCleanup' of 'TestCase' object "
+                            "needs an argument")
+        elif 'function' in kwargs:
+            function = kwargs.pop('function')
+            self, *args = args
+        else:
+            raise TypeError('addCleanup expected at least 1 positional '
+                            'argument, got %d' % (len(args)-1))
+        args = tuple(args)
+
         self._cleanups.append((function, args, kwargs))
 
     def setUp(self):
diff --git a/Lib/weakref.py b/Lib/weakref.py
index 753f07291e..59b3aa5621 100644
--- a/Lib/weakref.py
+++ b/Lib/weakref.py
@@ -527,7 +527,27 @@ class finalize:
     class _Info:
         __slots__ = ("weakref", "func", "args", "kwargs", "atexit", "index")
 
-    def __init__(self, obj, func, *args, **kwargs):
+    def __init__(*args, **kwargs):
+        if len(args) >= 3:
+            self, obj, func, *args = args
+        elif not args:
+            raise TypeError("descriptor '__init__' of 'finalize' object "
+                            "needs an argument")
+        else:
+            if 'func' not in kwargs:
+                raise TypeError('finalize expected at least 2 positional '
+                                'arguments, got %d' % (len(args)-1))
+            func = kwargs.pop('func')
+            if len(args) >= 2:
+                self, obj, *args = args
+            else:
+                if 'obj' not in kwargs:
+                    raise TypeError('finalize expected at least 2 positional '
+                                    'arguments, got %d' % (len(args)-1))
+                obj = kwargs.pop('obj')
+                self, *args = args
+        args = tuple(args)
+
         if not self._registered_with_atexit:
             # We may register the exit function more than once because
             # of a thread race, but that is harmless
diff --git a/Misc/NEWS.d/next/Library/2019-03-31-10-21-54.bpo-36492.f7vyUs.rst b/Misc/NEWS.d/next/Library/2019-03-31-10-21-54.bpo-36492.f7vyUs.rst
new file mode 100644
index 0000000000..749e2a87ab
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-03-31-10-21-54.bpo-36492.f7vyUs.rst
@@ -0,0 +1,5 @@
+Arbitrary keyword arguments (even with names "self" and "func") can now be
+passed to some functions which should accept arbitrary keyword arguments and
+pass them to other function (for example partialmethod(), TestCase.addCleanup()
+and Profile.runcall()) if the required arguments are passed as positional
+arguments.