optimization: str(x) -> PyObject_Str(x)

[jbrockmendel]

AFAICT they are equivalent. Found a usage of PyObject_str here and it looks like the optimization isn't made in other places where we just do str(x).

I was happy to see that the usage of PyUnicode_Join was unnecessary.

[scoder]

Yes, they are equivalent.

The optimisation for the 1-argument case can follow this example:

cython/Cython/Compiler/Optimize.py

Line 2320 in 5578a9e

def _handle_simple_function_unicode(self, node, function, pos_args):

Note that this needs to behave "as expected" for the three language levels 2, 3str and 3, but I think that should be ok. IIRC, str() gets mapped to unicode() (which is already optimised) in LL-3, but not in LL-2/3str, where the new optimisation would apply.

[scoder]

Implemented in #3478.