gh-117709: Add vectorcall support for positional-only arguments of str()

[erlend-aasland]

Competing PR to gh-117725.

• Issue: PyUnicode_Type needs vectorcall. #117709

[erlend-aasland]

The speedups are as with #117725, but only for the positional-only cases. Summary of the benchmarks¹:

• str(): 2x faster (not that it matters much; it's not a very interesting use-case)
• str(x): no change
• str(x, enc): 2x faster
• str(x, enc, err): 3x faster
• fallback for any case with keyword args: no change

Footnotes

1. release build on macOS. ↩

[vstinner]

I prefer this PR over #117725 which is way more complex.

[vstinner]

You may add a comment to mention that this function is a fast-path for positional-only cases.

[corona10]

I personally prefer this one :)
Do we have enough tests for positional arguments cases?

[erlend-aasland]

I personally prefer this one :) Do we have enough tests for positional arguments cases?

Well, we could add something like this:

diff --git a/Lib/test/test_str.py b/Lib/test/test_str.py
index b4927113db..ea37eb5d96 100644
--- a/Lib/test/test_str.py
+++ b/Lib/test/test_str.py
@@ -2651,6 +2651,24 @@ def test_check_encoding_errors(self):
         proc = assert_python_failure('-X', 'dev', '-c', code)
         self.assertEqual(proc.rc, 10, proc)
 
+    def test_str_invalid_call(self):
+        check = lambda *a, **kw: self.assertRaises(TypeError, str, *a, **kw)
+
+        # too many args
+        check(1, "", "", 1)
+
+        # no such kw arg
+        check(test=1)
+
+        # 'encoding' must be str
+        check(1, encoding=1)
+        check(1, 1)
+
+        # 'errors' must be str
+        check(1, errors=1)
+        check(1, "", errors=1)
+        check(1, 1, 1)
+
 
 class StringModuleTest(unittest.TestCase):
     def test_formatter_parser(self):

UPDATE: added in 8138db4

[corona10]

lgtm

[vstinner]

LGTM. I added a suggestion.

I'm not sure that arg_as_utf8() helper is strictly needed, you can keep it or inline it, it's up to you ;-)

[erlend-aasland]

Thank you so much for the reviews, Donghee and Victor!