Issue #20184: Add signature introspection for 30 of the builtins

Also adds a test to test_inspect to track progress on builtin
introspection support, to ensure it doesn't regress in the future.

Lib/test/test_inspect.py

+import builtins
 import collections
 import datetime
 import functools
@@ -23,7 +24,7 @@ except ImportError:
     ThreadPoolExecutor = None
 
 from test.support import run_unittest, TESTFN, DirsOnSysPath, cpython_only
-from test.support import MISSING_C_DOCSTRINGS
+from test.support import MISSING_C_DOCSTRINGS, cpython_only
 from test.script_helper import assert_python_ok, assert_python_failure
 from test import inspect_fodder as mod
 from test import inspect_fodder2 as mod2
@@ -1623,6 +1624,57 @@ class MyParameter(inspect.Parameter):
     # used in test_signature_object_pickle
     pass
 
+    @cpython_only
+    @unittest.skipIf(MISSING_C_DOCSTRINGS,
+                     "Signature information for builtins requires docstrings")
+    def test_builtins_have_signatures(self):
+        # This checks all builtin callables in CPython have signatures
+        # A few have signatures Signature can't yet handle, so we skip those
+        # since they will have to wait until PEP 457 adds the required
+        # introspection support to the inspect module
+        # Some others also haven't been converted yet for various other
+        # reasons, so we also skip those for the time being, but design
+        # the test to fail in order to indicate when it needs to be
+        # updated.
+        no_signature = set()
+        # These need PEP 457 groups
+        needs_groups = ["range", "slice", "dir", "getattr",
+                        "next", "iter", "vars"]
+        no_signature |= needs_groups
+        # These need PEP 457 groups or a signature change to accept None
+        needs_semantic_update = ["round"]
+        no_signature |= needs_semantic_update
+        # These need *args support in Argument Clinic
+        needs_varargs = ["min", "max", "print", "__build_class__"]
+        no_signature |= needs_varargs
+        # These simply weren't covered in the initial AC conversion
+        # for builtin callables
+        not_converted_yet = ["open", "__import__"]
+        no_signature |= not_converted_yet
+        # These builtin types are expected to provide introspection info
+        types_with_signatures = set()
+        # Check the signatures we expect to be there
+        ns = vars(builtins)
+        for name, obj in sorted(ns.items()):
+            if not callable(obj):
+                continue
+            # The builtin types haven't been converted to AC yet
+            if isinstance(obj, type) and (name not in types_with_signatures):
+                # Note that this also skips all the exception types
+                no_signature.append(name)
+            if (name in no_signature):
+                # Not yet converted
+                continue
+            with self.subTest(builtin=name):
+                self.assertIsNotNone(inspect.signature(obj))
+        # Check callables that haven't been converted don't claim a signature
+        # This ensures this test will start failing as more signatures are
+        # added, so the affected items can be moved into the scope of the
+        # regression test above
+        for name in no_signature:
+            with self.subTest(builtin=name):
+                self.assertIsNone(ns[name].__text_signature__)
+
 
 class TestSignatureObject(unittest.TestCase):
     @staticmethod

Misc/NEWS

@@ -10,6 +10,9 @@ Release date: TBA
 Core and Builtins
 -----------------
 
+- Issue #20184: Argument Clinic based signature introspection added for
+  30 of the builtin functions.
+
 - Issue #22116: C functions and methods (of the 'builtin_function_or_method'
   type) can now be weakref'ed.  Patch by Wei Wu.