inspect: Fix getcallargs() to fail correctly if more than 3 args are missing.

Patch by Jeremiah Lowin. Closes #20817.

Lib/inspect.py

@@ -1127,7 +1127,7 @@ def _missing_arguments(f_name, argnames, pos, values):
     elif missing == 2:
         s = "{} and {}".format(*names)
     else:
-        tail = ", {} and {}".format(names[-2:])
+        tail = ", {} and {}".format(*names[-2:])
         del names[-2:]
         s = ", ".join(names) + tail
     raise TypeError("%s() missing %i required %s argument%s: %s" %

Lib/test/test_inspect.py

@@ -1216,6 +1216,12 @@ class TestGetcallargsFunctions(unittest.TestCase):
             inspect.getcallargs(f5)
 
 
+        # issue20817:
+        def f6(a, b, c):
+            pass
+        with self.assertRaisesRegex(TypeError, "'a', 'b' and 'c'"):
+            inspect.getcallargs(f6)
+
 class TestGetcallargsMethods(TestGetcallargsFunctions):
 
     def setUp(self):

Misc/NEWS

@@ -116,6 +116,9 @@ Library
 - Issue #20816: Fix inspect.getcallargs() to raise correct TypeError for
   missing keyword-only arguments. Patch by Jeremiah Lowin.
 
+- Issue #20817: Fix inspect.getcallargs() to fail correctly if more
+  than 3 arguments are missing. Patch by Jeremiah Lowin.
+
 Documentation
 -------------