bpo-37116: Use PEP 570 syntax for positional-only parameters. (GH-13700)

Doc/library/collections.rst

@@ -1140,7 +1140,7 @@ variants of :func:`functools.lru_cache`::
     class LRU(OrderedDict):
         'Limit size, evicting the least recently looked-up key when full'
 
-        def __init__(self, maxsize=128, *args, **kwds):
+        def __init__(self, maxsize=128, /, *args, **kwds):
             self.maxsize = maxsize
             super().__init__(*args, **kwds)
 

Doc/library/contextlib.rst

@@ -637,7 +637,7 @@ even further by means of a small helper class::
    from contextlib import ExitStack
 
    class Callback(ExitStack):
-       def __init__(self, callback, *args, **kwds):
+       def __init__(self, callback, /, *args, **kwds):
            super(Callback, self).__init__()
            self.callback(callback, *args, **kwds)
 

Doc/library/email.headerregistry.rst

@@ -107,7 +107,7 @@ headers.
    method if it wishes to set additional attributes beyond those provided by
    ``BaseHeader`` itself.  Such an ``init`` method should look like this::
 
-       def init(self, *args, **kw):
+       def init(self, /, *args, **kw):
            self._myattr = kw.pop('myattr')
            super().init(*args, **kw)
 

Doc/library/functools.rst

@@ -221,7 +221,7 @@ The :mod:`functools` module defines the following functions:
       Returning NotImplemented from the underlying comparison function for
       unrecognised types is now supported.
 
-.. function:: partial(func, *args, **keywords)
+.. function:: partial(func, /, *args, **keywords)
 
    Return a new :ref:`partial object<partial-objects>` which when called
    will behave like *func* called with the positional arguments *args*
@@ -230,7 +230,7 @@ The :mod:`functools` module defines the following functions:
    supplied, they extend and override *keywords*.
    Roughly equivalent to::
 
-      def partial(func, *args, **keywords):
+      def partial(func, /, *args, **keywords):
           def newfunc(*fargs, **fkeywords):
               newkeywords = {**keywords, **fkeywords}
               return func(*args, *fargs, **newkeywords)

Doc/library/inspect.rst

@@ -1022,7 +1022,7 @@ Classes and functions
    metatype is in use, cls will be the first element of the tuple.
 
 
-.. function:: getcallargs(func, *args, **kwds)
+.. function:: getcallargs(func, /, *args, **kwds)
 
    Bind the *args* and *kwds* to the argument names of the Python function or
    method *func*, as if it was called with them. For bound methods, bind also the

Doc/library/operator.rst

@@ -339,7 +339,7 @@ expect a function argument.
       [('orange', 1), ('banana', 2), ('apple', 3), ('pear', 5)]
 
 
-.. function:: methodcaller(name[, args...])
+.. function:: methodcaller(name, /, *args, **kwargs)
 
    Return a callable object that calls the method *name* on its operand.  If
    additional arguments and/or keyword arguments are given, they will be given
@@ -352,7 +352,7 @@ expect a function argument.
 
    Equivalent to::
 
-      def methodcaller(name, *args, **kwargs):
+      def methodcaller(name, /, *args, **kwargs):
           def caller(obj):
               return getattr(obj, name)(*args, **kwargs)
           return caller

Doc/library/string.rst

@@ -88,7 +88,7 @@ implementation as the built-in :meth:`~str.format` method.
 
    The :class:`Formatter` class has the following public methods:
 
-   .. method:: format(format_string, *args, **kwargs)
+   .. method:: format(format_string, /, *args, **kwargs)
 
       The primary API method.  It takes a format string and
       an arbitrary set of positional and keyword arguments.
@@ -720,7 +720,7 @@ these rules.  The methods of :class:`Template` are:
    The constructor takes a single argument which is the template string.
 
 
-   .. method:: substitute(mapping, **kwds)
+   .. method:: substitute(mapping={}, /, **kwds)
 
       Performs the template substitution, returning a new string.  *mapping* is
       any dictionary-like object with keys that match the placeholders in the
@@ -729,7 +729,7 @@ these rules.  The methods of :class:`Template` are:
       and there are duplicates, the placeholders from *kwds* take precedence.
 
 
-   .. method:: safe_substitute(mapping, **kwds)
+   .. method:: safe_substitute(mapping={}, /, **kwds)
 
       Like :meth:`substitute`, except that if placeholders are missing from
       *mapping* and *kwds*, instead of raising a :exc:`KeyError` exception, the

Doc/library/types.rst

@@ -327,7 +327,7 @@ Additional Utility Classes and Functions
    The type is roughly equivalent to the following code::
 
        class SimpleNamespace:
-           def __init__(self, **kwargs):
+           def __init__(self, /, **kwargs):
                self.__dict__.update(kwargs)
 
            def __repr__(self):

Doc/library/unittest.mock-examples.rst

@@ -848,7 +848,7 @@ Here's an example implementation:
 
     >>> from copy import deepcopy
     >>> class CopyingMock(MagicMock):
-    ...     def __call__(self, *args, **kwargs):
+    ...     def __call__(self, /, *args, **kwargs):
     ...         args = deepcopy(args)
     ...         kwargs = deepcopy(kwargs)
     ...         return super(CopyingMock, self).__call__(*args, **kwargs)
@@ -1042,7 +1042,7 @@ that it takes arbitrary keyword arguments (``**kwargs``) which are then passed
 onto the mock constructor:
 
     >>> class Subclass(MagicMock):
-    ...     def _get_child_mock(self, **kwargs):
+    ...     def _get_child_mock(self, /, **kwargs):
     ...         return MagicMock(**kwargs)
     ...
     >>> mymock = Subclass()

Doc/library/unittest.rst

@@ -1456,7 +1456,7 @@ Test cases
 
       .. versionadded:: 3.1
 
-   .. classmethod:: addClassCleanup(function, *args, **kwargs)
+   .. classmethod:: addClassCleanup(function, /, *args, **kwargs)
 
       Add a function to be called after :meth:`tearDownClass` to cleanup
       resources used during the test class. Functions will be called in reverse
@@ -2313,7 +2313,7 @@ To add cleanup code that must be run even in the case of an exception, use
 ``addModuleCleanup``:
 
 
-.. function:: addModuleCleanup(function, *args, **kwargs)
+.. function:: addModuleCleanup(function, /, *args, **kwargs)
 
    Add a function to be called after :func:`tearDownModule` to cleanup
    resources used during the test class. Functions will be called in reverse

Doc/library/weakref.rst

@@ -396,7 +396,7 @@ the referent is accessed::
    import weakref
 
    class ExtendedRef(weakref.ref):
-       def __init__(self, ob, callback=None, **annotations):
+       def __init__(self, ob, callback=None, /, **annotations):
            super(ExtendedRef, self).__init__(ob, callback)
            self.__counter = 0
            for k, v in annotations.items():

Doc/whatsnew/3.8.rst

@@ -941,8 +941,7 @@ Deprecated
     :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`.
+  - *function* in :meth:`unittest.TestCase.addCleanup`.
   - *fn* in the :meth:`~concurrent.futures.Executor.submit` method of
     :class:`concurrent.futures.ThreadPoolExecutor` and
     :class:`concurrent.futures.ProcessPoolExecutor`.

Lib/_collections_abc.py

@@ -821,21 +821,12 @@ class MutableMapping(Mapping):
         except KeyError:
             pass
 
-    def update(*args, **kwds):
+    def update(self, other=(), /, **kwds):
         ''' D.update([E, ]**F) -> None.  Update D from mapping/iterable E and F.
             If E present and has a .keys() method, does:     for k in E: D[k] = E[k]
             If E present and lacks .keys() method, does:     for (k, v) in E: D[k] = v
             In either case, this is followed by: for k, v in F.items(): D[k] = v
         '''
-        if not args:
-            raise TypeError("descriptor 'update' of 'MutableMapping' object "
-                            "needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('update expected at most 1 arguments, got %d' %
-                            len(args))
-        if args:
-            other = args[0]
         if isinstance(other, Mapping):
             for key in other:
                 self[key] = other[key]

Lib/_py_abc.py

@@ -32,7 +32,7 @@ class ABCMeta(type):
     #       external code.
     _abc_invalidation_counter = 0
 
-    def __new__(mcls, name, bases, namespace, **kwargs):
+    def __new__(mcls, name, bases, namespace, /, **kwargs):
         cls = super().__new__(mcls, name, bases, namespace, **kwargs)
         # Compute set of abstract method names
         abstracts = {name

Lib/_threading_local.py

@@ -56,7 +56,7 @@ You can create custom local objects by subclassing the local class:
 
   >>> class MyLocal(local):
   ...     number = 2
-  ...     def __init__(self, **kw):
+  ...     def __init__(self, /, **kw):
   ...         self.__dict__.update(kw)
   ...     def squared(self):
   ...         return self.number ** 2
@@ -204,7 +204,7 @@ def _patch(self):
 class local:
     __slots__ = '_local__impl', '__dict__'
 
-    def __new__(cls, *args, **kw):
+    def __new__(cls, /, *args, **kw):
         if (args or kw) and (cls.__init__ is object.__init__):
             raise TypeError("Initialization arguments are not supported")
         self = object.__new__(cls)

Lib/collections/__init__.py

@@ -93,16 +93,10 @@ class OrderedDict(dict):
     # Individual links are kept alive by the hard reference in self.__map.
     # Those hard references disappear when a key is deleted from an OrderedDict.
 
-    def __init__(*args, **kwds):
+    def __init__(self, other=(), /, **kwds):
         '''Initialize an ordered dictionary.  The signature is the same as
         regular dictionaries.  Keyword argument order is preserved.
         '''
-        if not args:
-            raise TypeError("descriptor '__init__' of 'OrderedDict' object "
-                            "needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('expected at most 1 arguments, got %d' % len(args))
         try:
             self.__root
         except AttributeError:
@@ -110,7 +104,7 @@ class OrderedDict(dict):
             self.__root = root = _proxy(self.__hardroot)
             root.prev = root.next = root
             self.__map = {}
-        self.__update(*args, **kwds)
+        self.__update(other, **kwds)
 
     def __setitem__(self, key, value,
                     dict_setitem=dict.__setitem__, proxy=_proxy, Link=_Link):
@@ -413,8 +407,8 @@ def namedtuple(typename, field_names, *, rename=False, defaults=None, module=Non
     _make.__func__.__doc__ = (f'Make a new {typename} object from a sequence '
                               'or iterable')
 
-    def _replace(_self, **kwds):
-        result = _self._make(_map(kwds.pop, field_names, _self))
+    def _replace(self, /, **kwds):
+        result = self._make(_map(kwds.pop, field_names, self))
         if kwds:
             raise ValueError(f'Got unexpected field names: {list(kwds)!r}')
         return result
@@ -543,7 +537,7 @@ class Counter(dict):
     #   http://code.activestate.com/recipes/259174/
     #   Knuth, TAOCP Vol. II section 4.6.3
 
-    def __init__(*args, **kwds):
+    def __init__(self, iterable=None, /, **kwds):
         '''Create a new, empty Counter object.  And if given, count elements
         from an input iterable.  Or, initialize the count from another mapping
         of elements to their counts.
@@ -554,14 +548,8 @@ class Counter(dict):
         >>> c = Counter(a=4, b=2)                   # a new counter from keyword args
 
         '''
-        if not args:
-            raise TypeError("descriptor '__init__' of 'Counter' object "
-                            "needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('expected at most 1 arguments, got %d' % len(args))
         super(Counter, self).__init__()
-        self.update(*args, **kwds)
+        self.update(iterable, **kwds)
 
     def __missing__(self, key):
         'The count of elements not in the Counter is zero.'
@@ -617,7 +605,7 @@ class Counter(dict):
         raise NotImplementedError(
             'Counter.fromkeys() is undefined.  Use Counter(iterable) instead.')
 
-    def update(*args, **kwds):
+    def update(self, iterable=None, /, **kwds):
         '''Like dict.update() but add counts instead of replacing them.
 
         Source can be an iterable, a dictionary, or another Counter instance.
@@ -637,13 +625,6 @@ class Counter(dict):
         # contexts.  Instead, we implement straight-addition.  Both the inputs
         # and outputs are allowed to contain zero and negative counts.
 
-        if not args:
-            raise TypeError("descriptor 'update' of 'Counter' object "
-                            "needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('expected at most 1 arguments, got %d' % len(args))
-        iterable = args[0] if args else None
         if iterable is not None:
             if isinstance(iterable, _collections_abc.Mapping):
                 if self:
@@ -657,7 +638,7 @@ class Counter(dict):
         if kwds:
             self.update(kwds)
 
-    def subtract(*args, **kwds):
+    def subtract(self, iterable=None, /, **kwds):
         '''Like dict.update() but subtracts counts instead of replacing them.
         Counts can be reduced below zero.  Both the inputs and outputs are
         allowed to contain zero and negative counts.
@@ -673,13 +654,6 @@ class Counter(dict):
         -1
 
         '''
-        if not args:
-            raise TypeError("descriptor 'subtract' of 'Counter' object "
-                            "needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('expected at most 1 arguments, got %d' % len(args))
-        iterable = args[0] if args else None
         if iterable is not None:
             self_get = self.get
             if isinstance(iterable, _collections_abc.Mapping):
@@ -1141,7 +1115,7 @@ class UserList(_collections_abc.MutableSequence):
     def count(self, item): return self.data.count(item)
     def index(self, item, *args): return self.data.index(item, *args)
     def reverse(self): self.data.reverse()
-    def sort(self, *args, **kwds): self.data.sort(*args, **kwds)
+    def sort(self, /, *args, **kwds): self.data.sort(*args, **kwds)
     def extend(self, other):
         if isinstance(other, UserList):
             self.data.extend(other.data)
@@ -1240,7 +1214,7 @@ class UserString(_collections_abc.Sequence):
         if isinstance(sub, UserString):
             sub = sub.data
         return self.data.find(sub, start, end)
-    def format(self, *args, **kwds):
+    def format(self, /, *args, **kwds):
         return self.data.format(*args, **kwds)
     def format_map(self, mapping):
         return self.data.format_map(mapping)

Lib/contextlib.py

@@ -377,8 +377,7 @@ class _BaseExitStack:
         return MethodType(cm_exit, cm)
 
     @staticmethod
-    def _create_cb_wrapper(*args, **kwds):
-        callback, *args = args
+    def _create_cb_wrapper(callback, /, *args, **kwds):
         def _exit_wrapper(exc_type, exc, tb):
             callback(*args, **kwds)
         return _exit_wrapper
@@ -553,8 +552,7 @@ class AsyncExitStack(_BaseExitStack, AbstractAsyncContextManager):
         return MethodType(cm_exit, cm)
 
     @staticmethod
-    def _create_async_cb_wrapper(*args, **kwds):
-        callback, *args = args
+    def _create_async_cb_wrapper(callback, /, *args, **kwds):
         async def _exit_wrapper(exc_type, exc, tb):
             await callback(*args, **kwds)
         return _exit_wrapper

Lib/dataclasses.py

@@ -962,10 +962,7 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen):
     return cls
 
 
-# _cls should never be specified by keyword, so start it with an
-# underscore.  The presence of _cls is used to detect if this
-# decorator is being called with parameters or not.
-def dataclass(_cls=None, *, init=True, repr=True, eq=True, order=False,
+def dataclass(cls=None, /, *, init=True, repr=True, eq=True, order=False,
               unsafe_hash=False, frozen=False):
     """Returns the same class as was passed in, with dunder methods
     added based on the fields defined in the class.
@@ -983,12 +980,12 @@ def dataclass(_cls=None, *, init=True, repr=True, eq=True, order=False,
         return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)
 
     # See if we're being called as @dataclass or @dataclass().
-    if _cls is None:
+    if cls is None:
         # We're called with parens.
         return wrap
 
     # We're called as @dataclass without parens.
-    return wrap(_cls)
+    return wrap(cls)
 
 
 def fields(class_or_instance):

Lib/functools.py

@@ -273,15 +273,9 @@ class partial:
 
     __slots__ = "func", "args", "keywords", "__dict__", "__weakref__"
 
-    def __new__(*args, **keywords):
-        if not args:
-            raise TypeError("descriptor '__new__' of partial needs an argument")
-        if len(args) < 2:
-            raise TypeError("type 'partial' takes at least one argument")
-        cls, func, *args = args
+    def __new__(cls, func, /, *args, **keywords):
         if not callable(func):
             raise TypeError("the first argument must be callable")
-        args = tuple(args)
 
         if hasattr(func, "func"):
             args = func.args + args
@@ -295,10 +289,7 @@ class partial:
         self.keywords = keywords
         return self
 
-    def __call__(*args, **keywords):
-        if not args:
-            raise TypeError("descriptor '__call__' of partial needs an argument")
-        self, *args = args
+    def __call__(self, /, *args, **keywords):
         keywords = {**self.keywords, **keywords}
         return self.func(*self.args, *args, **keywords)
 
@@ -402,8 +393,7 @@ class partialmethod(object):
                                     keywords=keywords)
 
     def _make_unbound_method(self):
-        def _method(*args, **keywords):
-            cls_or_self, *args = args
+        def _method(cls_or_self, /, *args, **keywords):
             keywords = {**self.keywords, **keywords}
             return self.func(cls_or_self, *self.args, *args, **keywords)
         _method.__isabstractmethod__ = self.__isabstractmethod__

Lib/idlelib/debugger_r.py

@@ -299,7 +299,7 @@ class IdbProxy:
         self.conn = conn
         self.shell = shell
 
-    def call(self, methodname, *args, **kwargs):
+    def call(self, methodname, /, *args, **kwargs):
         ##print("*** IdbProxy.call %s %s %s" % (methodname, args, kwargs))
         value = self.conn.remotecall(self.oid, methodname, args, kwargs)
         ##print("*** IdbProxy.call %s returns %r" % (methodname, value))

Lib/idlelib/rpc.py

@@ -603,7 +603,7 @@ class MethodProxy(object):
         self.oid = oid
         self.name = name
 
-    def __call__(self, *args, **kwargs):
+    def __call__(self, /, *args, **kwargs):
         value = self.sockio.remotecall(self.oid, self.name, args, kwargs)
         return value
 

Lib/inspect.py

@@ -1329,14 +1329,12 @@ def _too_many(f_name, args, kwonly, varargs, defcount, given, values):
             (f_name, sig, "s" if plural else "", given, kwonly_sig,
              "was" if given == 1 and not kwonly_given else "were"))
 
-def getcallargs(*func_and_positional, **named):
+def getcallargs(func, /, *positional, **named):
     """Get the mapping of arguments to values.
 
     A dict is returned, with keys the function argument names (including the
     names of the * and ** arguments, if any), and values the respective bound
     values from 'positional' and 'named'."""
-    func = func_and_positional[0]
-    positional = func_and_positional[1:]
     spec = getfullargspec(func)
     args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, ann = spec
     f_name = func.__name__
@@ -3027,19 +3025,19 @@ class Signature:
 
         return self._bound_arguments_cls(self, arguments)
 
-    def bind(*args, **kwargs):
+    def bind(self, /, *args, **kwargs):
         """Get a BoundArguments object, that maps the passed `args`
         and `kwargs` to the function's signature.  Raises `TypeError`
         if the passed arguments can not be bound.
         """
-        return args[0]._bind(args[1:], kwargs)
+        return self._bind(args, kwargs)
 
-    def bind_partial(*args, **kwargs):
+    def bind_partial(self, /, *args, **kwargs):
         """Get a BoundArguments object, that partially maps the
         passed `args` and `kwargs` to the function's signature.
         Raises `TypeError` if the passed arguments can not be bound.
         """
-        return args[0]._bind(args[1:], kwargs, partial=True)
+        return self._bind(args, kwargs, partial=True)
 
     def __reduce__(self):
         return (type(self),

Lib/multiprocessing/dummy/__init__.py

@@ -80,7 +80,7 @@ def freeze_support():
 #
 
 class Namespace(object):
-    def __init__(self, **kwds):
+    def __init__(self, /, **kwds):
         self.__dict__.update(kwds)
     def __repr__(self):
         items = list(self.__dict__.items())

Lib/multiprocessing/managers.py

@@ -615,13 +615,10 @@ class BaseManager(object):
         util.info('manager serving at %r', server.address)
         server.serve_forever()
 
-    def _create(*args, **kwds):
+    def _create(self, typeid, /, *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:
@@ -738,7 +735,7 @@ class BaseManager(object):
             )
 
         if create_method:
-            def temp(self, *args, **kwds):
+            def temp(self, /, *args, **kwds):
                 util.debug('requesting creation of a shared %r object', typeid)
                 token, exp = self._create(typeid, *args, **kwds)
                 proxy = proxytype(
@@ -978,7 +975,7 @@ def MakeProxyType(name, exposed, _cache={}):
     dic = {}
 
     for meth in exposed:
-        exec('''def %s(self, *args, **kwds):
+        exec('''def %s(self, /, *args, **kwds):
         return self._callmethod(%r, args, kwds)''' % (meth, meth), dic)
 
     ProxyType = type(name, (BaseProxy,), dic)
@@ -1017,7 +1014,7 @@ def AutoProxy(token, serializer, manager=None, authkey=None,
 #
 
 class Namespace(object):
-    def __init__(self, **kwds):
+    def __init__(self, /, **kwds):
         self.__dict__.update(kwds)
     def __repr__(self):
         items = list(self.__dict__.items())

Lib/multiprocessing/pool.py

@@ -154,7 +154,7 @@ class _PoolCache(dict):
     notification is done by the use of a queue that is provided when
     instantiating the cache.
     """
-    def __init__(self, *args, notifier=None, **kwds):
+    def __init__(self, /, *args, notifier=None, **kwds):
         self.notifier = notifier
         super().__init__(*args, **kwds)
 

Lib/operator.py

@@ -302,15 +302,11 @@ class methodcaller:
     """
     __slots__ = ('_name', '_args', '_kwargs')
 
-    def __init__(*args, **kwargs):
-        if len(args) < 2:
-            msg = "methodcaller needs at least one argument, the method name"
-            raise TypeError(msg)
-        self = args[0]
-        self._name = args[1]
+    def __init__(self, name, /, *args, **kwargs):
+        self._name = name
         if not isinstance(self._name, str):
             raise TypeError('method name must be a string')
-        self._args = args[2:]
+        self._args = args
         self._kwargs = kwargs
 
     def __call__(self, obj):

Lib/random.py

@@ -100,7 +100,7 @@ class Random(_random.Random):
         self.seed(x)
         self.gauss_next = None
 
-    def __init_subclass__(cls, **kwargs):
+    def __init_subclass__(cls, /, **kwargs):
         """Control how subclasses generate random integers.
 
         The algorithm a subclass can use depends on the random() and/or

Lib/string.py

@@ -52,6 +52,8 @@ def capwords(s, sep=None):
 import re as _re
 from collections import ChainMap as _ChainMap
 
+_sentinel_dict = {}
+
 class _TemplateMetaclass(type):
     pattern = r"""
     %(delim)s(?:
@@ -104,19 +106,11 @@ class Template(metaclass=_TemplateMetaclass):
         raise ValueError('Invalid placeholder in string: line %d, col %d' %
                          (lineno, colno))
 
-    def substitute(*args, **kws):
-        if not args:
-            raise TypeError("descriptor 'substitute' of 'Template' object "
-                            "needs an argument")
-        self, *args = args  # allow the "self" keyword be passed
-        if len(args) > 1:
-            raise TypeError('Too many positional arguments')
-        if not args:
+    def substitute(self, mapping=_sentinel_dict, /, **kws):
+        if mapping is _sentinel_dict:
             mapping = kws
         elif kws:
-            mapping = _ChainMap(kws, args[0])
-        else:
-            mapping = args[0]
+            mapping = _ChainMap(kws, mapping)
         # Helper function for .sub()
         def convert(mo):
             # Check the most common path first.
@@ -131,19 +125,11 @@ class Template(metaclass=_TemplateMetaclass):
                              self.pattern)
         return self.pattern.sub(convert, self.template)
 
-    def safe_substitute(*args, **kws):
-        if not args:
-            raise TypeError("descriptor 'safe_substitute' of 'Template' object "
-                            "needs an argument")
-        self, *args = args  # allow the "self" keyword be passed
-        if len(args) > 1:
-            raise TypeError('Too many positional arguments')
-        if not args:
+    def safe_substitute(self, mapping=_sentinel_dict, /, **kws):
+        if mapping is _sentinel_dict:
             mapping = kws
         elif kws:
-            mapping = _ChainMap(kws, args[0])
-        else:
-            mapping = args[0]
+            mapping = _ChainMap(kws, mapping)
         # Helper function for .sub()
         def convert(mo):
             named = mo.group('named') or mo.group('braced')
@@ -173,16 +159,7 @@ class Template(metaclass=_TemplateMetaclass):
 # The field name parser is implemented in _string.formatter_field_name_split
 
 class Formatter:
-    def format(*args, **kwargs):
-        if not args:
-            raise TypeError("descriptor 'format' of 'Formatter' object "
-                            "needs an argument")
-        self, *args = args  # allow the "self" keyword be passed
-        try:
-            format_string, *args = args # allow the "format_string" keyword be passed
-        except ValueError:
-            raise TypeError("format() missing 1 required positional "
-                            "argument: 'format_string'") from None
+    def format(self, format_string, /, *args, **kwargs):
         return self.vformat(format_string, args, kwargs)
 
     def vformat(self, format_string, args, kwargs):

Lib/test/support/script_helper.py

@@ -137,7 +137,7 @@ def run_python_until_end(*args, **env_vars):
     err = strip_python_stderr(err)
     return _PythonRunResult(rc, out, err), cmd_line
 
-def _assert_python(expected_success, *args, **env_vars):
+def _assert_python(expected_success, /, *args, **env_vars):
     res, cmd_line = run_python_until_end(*args, **env_vars)
     if (res.rc and expected_success) or (not res.rc and not expected_success):
         res.fail(cmd_line)

Lib/typing.py

@@ -283,7 +283,7 @@ class _Final:
 
     __slots__ = ('__weakref__',)
 
-    def __init_subclass__(self, *args, **kwds):
+    def __init_subclass__(self, /, *args, **kwds):
         if '_root' not in kwds:
             raise TypeError("Cannot subclass special typing classes")
 

Lib/unittest/case.py

@@ -86,23 +86,10 @@ def _id(obj):
 
 
 _module_cleanups = []
-def addModuleCleanup(*args, **kwargs):
+def addModuleCleanup(function, /, *args, **kwargs):
     """Same as addCleanup, except the cleanup items are called even if
     setUpModule fails (unlike tearDownModule)."""
-    if args:
-        function, *args = args
-    elif 'function' in kwargs:
-        function = kwargs.pop('function')
-        import warnings
-        warnings.warn("Passing 'function' as keyword argument is deprecated",
-                      DeprecationWarning, stacklevel=2)
-    else:
-        raise TypeError('addModuleCleanup expected at least 1 positional '
-                        'argument, got %d' % (len(args)-1))
-    args = tuple(args)
-
     _module_cleanups.append((function, args, kwargs))
-addModuleCleanup.__text_signature__ = '(function, /, *args, **kwargs)'
 
 
 def doModuleCleanups():
@@ -501,22 +488,11 @@ class TestCase(object):
         self._cleanups.append((function, args, kwargs))
     addCleanup.__text_signature__ = '($self, function, /, *args, **kwargs)'
 
-    def addClassCleanup(*args, **kwargs):
+    @classmethod
+    def addClassCleanup(cls, function, /, *args, **kwargs):
         """Same as addCleanup, except the cleanup items are called even if
         setUpClass fails (unlike tearDownClass)."""
-        if len(args) >= 2:
-            cls, function, *args = args
-        elif not args:
-            raise TypeError("descriptor 'addClassCleanup' of 'TestCase' object "
-                            "needs an argument")
-        else:
-            raise TypeError('addClassCleanup expected at least 1 positional '
-                            'argument, got %d' % (len(args)-1))
-        args = tuple(args)
-
         cls._class_cleanups.append((function, args, kwargs))
-    addClassCleanup.__text_signature__ = '($cls, function, /, *args, **kwargs)'
-    addClassCleanup = classmethod(addClassCleanup)
 
     def setUp(self):
         "Hook method for setting up the test fixture before exercising it."

Lib/unittest/test/test_runner.py

@@ -410,14 +410,13 @@ class TestModuleCleanUp(unittest.TestCase):
 
         class Module(object):
             unittest.addModuleCleanup(cleanup, 1, 2, function='hello')
-            with self.assertWarns(DeprecationWarning):
+            with self.assertRaises(TypeError):
                 unittest.addModuleCleanup(function=cleanup, arg='hello')
             with self.assertRaises(TypeError):
                 unittest.addModuleCleanup()
         unittest.case.doModuleCleanups()
         self.assertEqual(cleanups,
-                         [((), {'arg': 'hello'}),
-                          ((1, 2), {'function': 'hello'})])
+                         [((1, 2), {'function': 'hello'})])
 
     def test_run_module_cleanUp(self):
         blowUp = True

Lib/weakref.py

@@ -99,13 +99,7 @@ class WeakValueDictionary(_collections_abc.MutableMapping):
     # objects are unwrapped on the way out, and we always wrap on the
     # way in).
 
-    def __init__(*args, **kw):
-        if not args:
-            raise TypeError("descriptor '__init__' of 'WeakValueDictionary' "
-                            "object needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('expected at most 1 arguments, got %d' % len(args))
+    def __init__(self, other=(), /, **kw):
         def remove(wr, selfref=ref(self), _atomic_removal=_remove_dead_weakref):
             self = selfref()
             if self is not None:
@@ -120,7 +114,7 @@ class WeakValueDictionary(_collections_abc.MutableMapping):
         self._pending_removals = []
         self._iterating = set()
         self.data = d = {}
-        self.update(*args, **kw)
+        self.update(other, **kw)
 
     def _commit_removals(self):
         l = self._pending_removals
@@ -287,24 +281,17 @@ class WeakValueDictionary(_collections_abc.MutableMapping):
         else:
             return o
 
-    def update(*args, **kwargs):
-        if not args:
-            raise TypeError("descriptor 'update' of 'WeakValueDictionary' "
-                            "object needs an argument")
-        self, *args = args
-        if len(args) > 1:
-            raise TypeError('expected at most 1 arguments, got %d' % len(args))
-        dict = args[0] if args else None
+    def update(self, other=None, /, **kwargs):
         if self._pending_removals:
             self._commit_removals()
         d = self.data
-        if dict is not None:
-            if not hasattr(dict, "items"):
-                dict = type({})(dict)
-            for key, o in dict.items():
+        if other is not None:
+            if not hasattr(other, "items"):
+                other = dict(other)
+            for key, o in other.items():
+                d[key] = KeyedRef(o, self._remove, key)
+        for key, o in kwargs.items():
             d[key] = KeyedRef(o, self._remove, key)
-        if len(kwargs):
-            self.update(kwargs)
 
     def valuerefs(self):
         """Return a list of weak references to the values.
@@ -488,7 +475,7 @@ class WeakKeyDictionary(_collections_abc.MutableMapping):
     def setdefault(self, key, default=None):
         return self.data.setdefault(ref(key, self._remove),default)
 
-    def update(self, dict=None, **kwargs):
+    def update(self, dict=None, /, **kwargs):
         d = self.data
         if dict is not None:
             if not hasattr(dict, "items"):