commit 445f1b35ce8461268438c8a6b327ddc764287e05
author Dong-hee Na <donghee.na92@gmail.com> Tue Jul 10 16:26:36 2018 +0900
committer INADA Naoki <methane@users.noreply.github.com> Tue Jul 10 16:26:36 2018 +0900
tree 7946f28321ff39563a8200ed7705a600f7ab521a
parent 7762e4d3872818272800dfbd8e1d8e3a689eb8f2

bpo-33967: Fix singledispatch raised IndexError when no args (GH-8184)

Lib/functools.py

diff --git a/Lib/functools.py b/Lib/functools.py
index d5f4393..b3428a4 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -817,8 +817,13 @@
         return func
 
     def wrapper(*args, **kw):
+        if not args:
+            raise TypeError(f'{funcname} requires at least '
+                            '1 positional argument')
+
         return dispatch(args[0].__class__)(*args, **kw)
 
+    funcname = getattr(func, '__name__', 'singledispatch function')
     registry[object] = func
     wrapper.register = register
     wrapper.dispatch = dispatch