bpo-36492: Deprecate passing some arguments as keyword arguments. (GH-12637)

Deprecated passing the following arguments as keyword arguments:

- "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 the create() method of multiprocessing.managers.Server
  and multiprocessing.managers.SharedMemoryServer.
- "obj" in weakref.finalize().

Also allowed to pass arbitrary keyword arguments (even "self" and "func")
if the above arguments are passed as positional argument.

Author: serhiy-storchaka

Doc/whatsnew/3.8.rst

@@ -594,6 +594,29 @@ Deprecated
   version they will be errors.
   (Contributed by Serhiy Storchaka in :issue:`36048`.)
 
+* Deprecated passing the following arguments as keyword arguments:
+
+  - *func* in :func:`functools.partialmethod`, :func:`weakref.finalize`,
+    :meth:`profile.Profile.runcall`, :meth:`cProfile.Profile.runcall`,
+    :meth:`bdb.Bdb.runcall`, :meth:`trace.Trace.runfunc` and
+    :func:`curses.wrapper`.
+  - *function* in :func:`unittest.addModuleCleanup` and
+    :meth:`unittest.TestCase.addCleanup`.
+  - *fn* in the :meth:`~concurrent.futures.Executor.submit` method of
+    :class:`concurrent.futures.ThreadPoolExecutor` and
+    :class:`concurrent.futures.ProcessPoolExecutor`.
+  - *callback* in :meth:`contextlib.ExitStack.callback`,
+    :meth:`contextlib.AsyncExitStack.callback` and
+    :meth:`contextlib.AsyncExitStack.push_async_callback`.
+  - *c* and *typeid* in the :meth:`~multiprocessing.managers.Server.create`
+    method of :class:`multiprocessing.managers.Server` and
+    :class:`multiprocessing.managers.SharedMemoryServer`.
+  - *obj* in :func:`weakref.finalize`.
+
+  In future releases of Python they will be :ref:`positional-only
+  <positional-only_parameter>`.
+  (Contributed by Serhiy Storchaka in :issue:`36492`.)
+
 
 API and Feature Removals
 ========================

Lib/bdb.py

@@ -618,11 +618,26 @@ def runctx(self, cmd, globals, locals):
 
     # 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
+            import warnings
+            warnings.warn("Passing 'func' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        else:
+            raise TypeError('runcall expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         self.reset()
         sys.settrace(self.trace_dispatch)
         res = None

Lib/cProfile.py

@@ -103,7 +103,22 @@ def runctx(self, cmd, globals, locals):
         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
+            import warnings
+            warnings.warn("Passing 'func' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        else:
+            raise TypeError('runcall expected at least 1 positional argument, '
+                            'got %d' % (len(args)-1))
+
         self.enable()
         try:
             return func(*args, **kw)

Lib/concurrent/futures/_base.py

@@ -544,7 +544,7 @@ def set_exception(self, exception):
 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
@@ -553,6 +553,19 @@ def submit(self, fn, *args, **kwargs):
         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' in kwargs:
+            import warnings
+            warnings.warn("Passing 'fn' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        else:
+            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):

Lib/concurrent/futures/process.py

@@ -594,7 +594,22 @@ def _adjust_process_count(self):
             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
+            import warnings
+            warnings.warn("Passing 'fn' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        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)

Lib/concurrent/futures/thread.py

@@ -142,7 +142,22 @@ def __init__(self, max_workers=None, thread_name_prefix='',
         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
+            import warnings
+            warnings.warn("Passing 'fn' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        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)

Lib/contextlib.py

@@ -377,7 +377,8 @@ def _create_exit_wrapper(cm, cm_exit):
         return MethodType(cm_exit, cm)
 
     @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
@@ -426,11 +427,26 @@ def enter_context(self, cm):
         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
+            import warnings
+            warnings.warn("Passing 'callback' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        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
@@ -536,7 +552,8 @@ def _create_async_exit_wrapper(cm, cm_exit):
         return MethodType(cm_exit, cm)
 
     @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
@@ -571,11 +588,26 @@ def push_async_exit(self, exit):
             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
+            import warnings
+            warnings.warn("Passing 'callback' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        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

Lib/curses/__init__.py

@@ -60,14 +60,25 @@ def start_color():
 # 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'
     as its first argument, followed by any other arguments passed to
     wrapper().
     """
 
+    if args:
+        func, *args = args
+    elif 'func' in kwds:
+        func = kwds.pop('func')
+        import warnings
+        warnings.warn("Passing 'func' as keyword argument is deprecated",
+                      DeprecationWarning, stacklevel=2)
+    else:
+        raise TypeError('wrapper expected at least 1 positional argument, '
+                        'got %d' % len(args))
+
     try:
         # Initialize curses
         stdscr = initscr()

Lib/functools.py

@@ -354,7 +354,23 @@ 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
+            import warnings
+            warnings.warn("Passing 'func' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        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))

Lib/multiprocessing/managers.py

@@ -358,10 +358,36 @@ def shutdown(self, c):
         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
+                import warnings
+                warnings.warn("Passing 'typeid' as keyword argument is deprecated",
+                              DeprecationWarning, stacklevel=2)
+            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
+                import warnings
+                warnings.warn("Passing 'c' as keyword argument is deprecated",
+                              DeprecationWarning, stacklevel=2)
+        args = tuple(args)
+
         with self.mutex:
             callable, exposed, method_to_typeid, proxytype = \
                       self.registry[typeid]
@@ -583,10 +609,13 @@ def _run_server(cls, registry, address, authkey, serializer, writer,
         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:
@@ -1261,15 +1290,25 @@ def __init__(self, *args, **kwargs):
                 _SharedMemoryTracker(f"shmm_{self.address}_{getpid()}")
             util.debug(f"SharedMemoryServer started by pid {getpid()}")
 
-        def create(self, c, typeid, *args, **kwargs):
+        def create(*args, **kwargs):
             """Create a new distributed-shared object (not backed by a shared
             memory block) and return its id to be used in a Proxy Object."""
             # Unless set up as a shared proxy, don't make shared_memory_context
             # a standard part of kwargs.  This makes things easier for supplying
             # simple functions.
+            if len(args) >= 3:
+                typeod = args[2]
+            elif 'typeid' in kwargs:
+                typeid = kwargs['typeid']
+            elif not args:
+                raise TypeError("descriptor 'create' of 'SharedMemoryServer' "
+                                "object needs an argument")
+            else:
+                raise TypeError('create expected at least 2 positional '
+                                'arguments, got %d' % (len(args)-1))
             if hasattr(self.registry[typeid][-1], "_shared_memory_proxy"):
                 kwargs['shared_memory_context'] = self.shared_memory_context
-            return Server.create(self, c, typeid, *args, **kwargs)
+            return Server.create(*args, **kwargs)
 
         def shutdown(self, c):
             "Call unlink() on all tracked shared memory, terminate the Server."

Lib/profile.py

@@ -425,7 +425,22 @@ def runctx(self, cmd, globals, locals):
         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
+            import warnings
+            warnings.warn("Passing 'func' as keyword argument is deprecated",
+                          DeprecationWarning, stacklevel=2)
+        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: