bpo-33967: singledispatch raises TypeError when no positional arguments #8184

corona10 · 2018-07-08T09:51:57Z

https://bugs.python.org/issue33967

methane · 2018-07-09T09:14:12Z

I think this is too much.

I think this is enough:

if not args:
    raise TypeError("singledispatch requires at least 1 positional argument")

doerwalter · 2018-07-09T10:09:20Z

True, both f(x=3) and g(*args) can be called with one argument, so shouldn't be rejected. I think @methane's solution does the right thing.

corona10 · 2018-07-09T10:13:06Z

Okay can I update this PR into suggested one?

corona10 · 2018-07-09T11:29:46Z

@doerwalter @methane

Updated! Please take a look!

methane · 2018-07-09T11:47:29Z

Lib/test/test_functools.py

+        with self.assertRaisesRegexp(TypeError, msg):
+            g()
+        with self.assertRaisesRegexp(TypeError, msg):
+            e()


Test seems too redundant for now.
TypeError happens always when no positional arguments.
How the generic function defined is not important.

methane · 2018-07-09T11:49:48Z

f"{func.__name__} requires at least 1 positional argument" may be better, if we can assume func.__name__ is available always.

I believe singledispatch requires positional argument by design, intentionally.
But I want @ambv review before merge.

corona10 · 2018-07-09T12:02:48Z

@methane
Thanks for the quick review.
Updated!
One more thing, we need to add tags needs backport to 3.7 / 3.6.

methane · 2018-07-09T12:14:48Z

Misc/NEWS.d/next/Library/2018-07-08-18-49-41.bpo-33967.lhaAez.rst

@@ -0,0 +1,2 @@
+Improve functools.singledispatch exception messages when calling without
+arguments


Error message is not important here. (We won't backport such improvements)

functools.singledispatch now raises TypeError instead of IndexError when no positional arguments are passed.

corona10 · 2018-07-09T13:46:39Z

@methane I've updated news

serhiy-storchaka · 2018-07-09T15:31:50Z

Lib/functools.py

@@ -817,6 +817,10 @@ def register(cls, func=None):
        return func

    def wrapper(*args, **kw):
+        if not args:
+            raise TypeError(f'{func.__name__} requires at least '


func can be not having the __name__ attribute in general case. This PR can break a code which use singledispatch() with custom callables.

Also this change creates a new reference to func linked to from wrapper. It may be better to keep a reference just to the name. E.g.

funcname = getattr(func, '__name__', 'singledispatch function') def wrapper(*args, **kw): # use funcname

corona10 · 2018-07-10T03:03:48Z

I fixed it

miss-islington · 2018-07-10T07:26:39Z

Thanks @corona10 for the PR, and @methane for merging it 🌮🎉.. I'm working now to backport this PR to: 3.6, 3.7.
🐍🍒⛏🤖

bedevere-bot · 2018-07-10T07:27:55Z

GH-8220 is a backport of this pull request to the 3.7 branch.

…H-8184) (cherry picked from commit 445f1b3) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

bedevere-bot · 2018-07-10T07:28:48Z

GH-8221 is a backport of this pull request to the 3.6 branch.

…H-8184) (cherry picked from commit 445f1b3) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

(cherry picked from commit 445f1b3) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

ZackerySpytz · 2018-07-12T02:13:05Z

Lib/test/test_functools.py

+        def f(*args):
+            pass
+        msg = 'f requires at least 1 positional argument'
+        with self.assertRaisesRegexp(TypeError, msg):


assertRaisesRegexp() is deprecated, so this test fails when test_functools is run with -Werror (see #8261).

corona10 requested review from ncoghlan and rhettinger as code owners July 8, 2018 09:51

the-knights-who-say-ni added the CLA signed label Jul 8, 2018

bedevere-bot added the awaiting review label Jul 8, 2018

methane requested a review from ambv July 9, 2018 09:15

corona10 force-pushed the bpo-33967 branch from 4f72f83 to 0962fd3 Compare July 9, 2018 11:28

methane reviewed Jul 9, 2018

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corona10 force-pushed the bpo-33967 branch from 0962fd3 to 7aad76b Compare July 9, 2018 12:00

methane changed the title ~~bpo-33967: Improve functools.singledispatch exception messages~~ bpo-33967: singledispatch raises TypeError when no positional arguments Jul 9, 2018

methane reviewed Jul 9, 2018

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methane added type-bug An unexpected behavior, bug, or error needs backport to 3.6 labels Jul 9, 2018

corona10 force-pushed the bpo-33967 branch from 7aad76b to 26d4234 Compare July 9, 2018 13:45

serhiy-storchaka reviewed Jul 9, 2018

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bpo-33967: functools.singledispatch now raises TypeError

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corona10 force-pushed the bpo-33967 branch from 26d4234 to 8730dbd Compare July 10, 2018 02:15

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methane merged commit 445f1b3 into python:master Jul 10, 2018

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miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Jul 10, 2018

bpo-33967: Fix singledispatch raised IndexError when no args (pythonG…

74b26a1

…H-8184) (cherry picked from commit 445f1b3) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

bedevere-bot removed the needs backport to 3.6 label Jul 10, 2018

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Jul 10, 2018

bpo-33967: Fix singledispatch raised IndexError when no args (pythonG…

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…H-8184) (cherry picked from commit 445f1b3) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

miss-islington added a commit that referenced this pull request Jul 10, 2018

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

df9f633

(cherry picked from commit 445f1b3) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

miss-islington added a commit that referenced this pull request Jul 10, 2018

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

6ceab46

(cherry picked from commit 445f1b3) Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

ZackerySpytz reviewed Jul 12, 2018

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bpo-33967: singledispatch raises TypeError when no positional arguments #8184

bpo-33967: singledispatch raises TypeError when no positional arguments #8184

corona10 commented Jul 8, 2018 •

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ZackerySpytz Jul 12, 2018

		@@ -0,0 +1,2 @@
		Improve functools.singledispatch exception messages when calling without
		arguments

bpo-33967: singledispatch raises TypeError when no positional arguments #8184

bpo-33967: singledispatch raises TypeError when no positional arguments #8184

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