bpo-36542: Allow to overwrite the signature for Python functions.

Lib/bdb.py

@@ -649,6 +649,7 @@ def runcall(*args, **kwds):
             self.quitting = True
             sys.settrace(None)
         return res
+    runcall.__text_signature__ = '($self, func, /, *args, **kwds)'
 
 
 def set_trace():

Lib/cProfile.py

@@ -124,6 +124,7 @@ def runcall(*args, **kw):
             return func(*args, **kw)
         finally:
             self.disable()
+    runcall.__text_signature__ = '($self, func, /, *args, **kw)'
 
     def __enter__(self):
         self.enable()

Lib/collections/__init__.py

@@ -1018,6 +1018,8 @@ def __init__(*args, **kwargs):
             self.update(dict)
         if kwargs:
             self.update(kwargs)
+    __init__.__text_signature__ = '($self, dict=None, /, **kwargs)'
+
     def __len__(self): return len(self.data)
     def __getitem__(self, key):
         if key in self.data:

Lib/concurrent/futures/_base.py

@@ -567,6 +567,7 @@ def submit(*args, **kwargs):
                             'got %d' % (len(args)-1))
 
         raise NotImplementedError()
+    submit.__text_signature__ = '($self, fn, /, *args, **kwargs)'
 
     def map(self, fn, *iterables, timeout=None, chunksize=1):
         """Returns an iterator equivalent to map(fn, iter).

Lib/concurrent/futures/process.py

@@ -630,6 +630,7 @@ def submit(*args, **kwargs):
 
             self._start_queue_management_thread()
             return f
+    submit.__text_signature__ = _base.Executor.submit.__text_signature__
     submit.__doc__ = _base.Executor.submit.__doc__
 
     def map(self, fn, *iterables, timeout=None, chunksize=1):

Lib/concurrent/futures/thread.py

@@ -174,6 +174,7 @@ def submit(*args, **kwargs):
             self._work_queue.put(w)
             self._adjust_thread_count()
             return f
+    submit.__text_signature__ = _base.Executor.submit.__text_signature__
     submit.__doc__ = _base.Executor.submit.__doc__
 
     def _adjust_thread_count(self):

Lib/contextlib.py

@@ -454,6 +454,7 @@ def callback(*args, **kwds):
         _exit_wrapper.__wrapped__ = callback
         self._push_exit_callback(_exit_wrapper)
         return callback  # Allow use as a decorator
+    callback.__text_signature__ = '($self, callback, /, *args, **kwds)'
 
     def _push_cm_exit(self, cm, cm_exit):
         """Helper to correctly register callbacks to __exit__ methods."""
@@ -615,6 +616,7 @@ def push_async_callback(*args, **kwds):
         _exit_wrapper.__wrapped__ = callback
         self._push_exit_callback(_exit_wrapper, False)
         return callback  # Allow use as a decorator
+    push_async_callback.__text_signature__ = '($self, callback, /, *args, **kwds)'
 
     async def aclose(self):
         """Immediately unwind the context stack."""

Lib/curses/__init__.py

@@ -110,3 +110,4 @@ def wrapper(*args, **kwds):
             echo()
             nocbreak()
             endwin()
+wrapper.__text_signature__ = '(func, /, *args, **kwds)'

Lib/functools.py

@@ -388,6 +388,7 @@ def __init__(*args, **keywords):
             self.func = func
             self.args = args
             self.keywords = keywords
+    __init__.__text_signature__ = '($self, func, /, *args, **keywords)'
 
     def __repr__(self):
         args = ", ".join(map(repr, self.args))

Lib/inspect.py

@@ -2119,7 +2119,7 @@ def _signature_from_builtin(cls, func, skip_bound_arg=True):
     return _signature_fromstr(cls, func, s, skip_bound_arg)
 
 
-def _signature_from_function(cls, func):
+def _signature_from_function(cls, func, skip_bound_arg=True):
     """Private helper: constructs Signature for the given python function."""
 
     is_duck_function = False
@@ -2131,6 +2131,10 @@ def _signature_from_function(cls, func):
             # of pure function:
             raise TypeError('{!r} is not a Python function'.format(func))
 
+    s = getattr(func, "__text_signature__", None)
+    if s:
+        return _signature_fromstr(cls, func, s, skip_bound_arg)
+
     Parameter = cls._parameter_cls
 
     # Parameter information.
@@ -2286,7 +2290,8 @@ def _signature_from_callable(obj, *,
     if isfunction(obj) or _signature_is_functionlike(obj):
         # If it's a pure Python function, or an object that is duck type
         # of a Python function (Cython functions, for instance), then:
-        return _signature_from_function(sigcls, obj)
+        return _signature_from_function(sigcls, obj,
+                                        skip_bound_arg=skip_bound_arg)
 
     if _signature_is_builtin(obj):
         return _signature_from_builtin(sigcls, obj,

Lib/multiprocessing/managers.py

@@ -419,6 +419,7 @@ def create(*args, **kwds):
 
         self.incref(c, ident)
         return ident, tuple(exposed)
+    create.__text_signature__ = '($self, c, typeid, /, *args, **kwds)'
 
     def get_methods(self, c, token):
         '''
@@ -1309,6 +1310,7 @@ def create(*args, **kwargs):
             if hasattr(self.registry[typeid][-1], "_shared_memory_proxy"):
                 kwargs['shared_memory_context'] = self.shared_memory_context
             return Server.create(*args, **kwargs)
+        create.__text_signature__ = '($self, c, typeid, /, *args, **kwargs)'
 
         def shutdown(self, c):
             "Call unlink() on all tracked shared memory, terminate the Server."

Lib/profile.py

@@ -447,6 +447,7 @@ def runcall(*args, **kw):
             return func(*args, **kw)
         finally:
             sys.setprofile(None)
+    runcall.__text_signature__ = '($self, func, /, *args, **kw)'
 
 
     #******************************************************************

Lib/test/test_inspect.py

@@ -3753,6 +3753,17 @@ def test_builtins_have_signatures(self):
             with self.subTest(builtin=name):
                 self.assertIsNone(obj.__text_signature__)
 
+    def test_python_function_override_signature(self):
+        def func(*args, **kwargs):
+            pass
+        func.__text_signature__ = '($self, a, b=1, *args, c, d=2, **kwargs)'
+        sig = inspect.signature(func)
+        self.assertIsNotNone(sig)
+        self.assertEqual(str(sig), '(self, /, a, b=1, *args, c, d=2, **kwargs)')
+        func.__text_signature__ = '($self, a, b=1, /, *args, c, d=2, **kwargs)'
+        sig = inspect.signature(func)
+        self.assertEqual(str(sig), '(self, a, b=1, /, *args, c, d=2, **kwargs)')
+
 
 class NTimesUnwrappable:
     def __init__(self, n):

Lib/trace.py

@@ -476,6 +476,7 @@ def runfunc(*args, **kw):
             if not self.donothing:
                 sys.settrace(None)
         return result
+    runfunc.__text_signature__ = '($self, func, /, *args, **kw)'
 
     def file_module_function_of(self, frame):
         code = frame.f_code

Lib/unittest/case.py

@@ -102,6 +102,7 @@ def addModuleCleanup(*args, **kwargs):
     args = tuple(args)
 
     _module_cleanups.append((function, args, kwargs))
+addModuleCleanup.__text_signature__ = '(function, /, *args, **kwargs)'
 
 
 def doModuleCleanups():
@@ -498,8 +499,8 @@ def addCleanup(*args, **kwargs):
         args = tuple(args)
 
         self._cleanups.append((function, args, kwargs))
+    addCleanup.__text_signature__ = '($self, function, /, *args, **kwargs)'
 
-    @classmethod
     def addClassCleanup(*args, **kwargs):
         """Same as addCleanup, except the cleanup items are called even if
         setUpClass fails (unlike tearDownClass)."""
@@ -514,6 +515,8 @@ def addClassCleanup(*args, **kwargs):
         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/weakref.py

@@ -569,6 +569,7 @@ def __init__(*args, **kwargs):
         info.index = next(self._index_iter)
         self._registry[self] = info
         finalize._dirty = True
+    __init__.__text_signature__ = '($self, obj, func, /, *args, **kwargs)'
 
     def __call__(self, _=None):
         """If alive then mark as dead and return func(*args, **kwargs);

Misc/NEWS.d/next/Library/2019-04-06-12-36-09.bpo-36542.Q0qyYV.rst

@@ -0,0 +1,2 @@
+The signature of Python functions can now be overridden by specifying the
+``__text_signature__`` attribute.