Keyword argument handling performance optimization.

[kkimdev]

Issue description

Keyword argument handling is slower than CPython.

CPython has an optimization that assumes the keyword name string objects are interned and performs pointer comparisons first instead https://github.com/python/cpython/blob/22424c02e51fab3b62cbe255d0b87d1b55b9a6c3/Python/ceval.c#L3975 .

Whereas Pybind constructs string objects and hashes them

pybind11/include/pybind11/pybind11.h

Line 518 in fb910ae

if (kwargs_in && arg_rec && arg_rec->name && PyDict_GetItemString(kwargs_in, arg_rec->name)) {

.

What do you think about having a similar optimization in Pybind?

Reproducible example code

void matmul(py::handle a,
            py::handle b,
            py::handle transpose_a,
            py::handle transpose_b,
            py::handle adjoint_a,
            py::handle adjoint_b,
            py::handle a_is_sparse,
            py::handle b_is_sparse,
            py::handle name) {
}
 
PYBIND11_MODULE(test, m) {
 m.def("matmul", &matmul,
       py::arg("a"),
       py::arg("b"),
       py::arg("transpose_a") = false,
       py::arg("transpose_b") = false,
       py::arg("adjoint_a") = false,
       py::arg("adjoint_b") = false,
       py::arg("a_is_sparse") = false,
       py::arg("b_is_sparse") = false,
       py::arg("name") = "");
}

test.matmul(1, 2, transpose_a = True)

[bstaletic]

This is interesting and worth looking into.

[EricCousineau-TRI]

Relates #2760 which benchmarking of alternative implementations, provided via @rwgk and @kkimdev - thanks!
#2760 (comment)

[XuehaiPan]

I'm encountering a similar issue. My focus is on caching compile-time string literals to enhance the efficiency of my program.

• PyUnicode_InternInPlace
• PyUnicode_InternFromString
• sys.intern