skip slow path on 3.8+

newsfragments/3742.changed.md

@@ -1 +1 @@
-Improve performance of `extract::<i64>` (and other integer types) by checking if types are a `PyLong` and if so avoiding calling `__index__()` before converting the value to an integer, matching the current behavior of `extract::<BigInt>()`. Gives performance improvement of around 30% for successful extraction.
+Improve performance of `extract::<i64>` (and other integer types) by avoiding call to `__index__()` converting the value to an integer for 3.8+. Gives performance improvement of around 30% for successful extraction.

src/conversions/std/num.rs

@@ -107,21 +107,32 @@ macro_rules! int_fits_c_long {
 
         impl<'source> FromPyObject<'source> for $rust_type {
             fn extract(obj: &'source PyAny) -> PyResult<Self> {
-                // fast path - checking for subclass of `int` just checks a bit in the type object
-                let val = if let Ok(long) = obj.downcast::<PyLong>() {
-                    err_if_invalid_value(obj.py(), -1, unsafe { ffi::PyLong_AsLong(long.as_ptr()) })
-                } else {
-                    unsafe {
-                        let num = ffi::PyNumber_Index(obj.as_ptr());
-                        if num.is_null() {
-                            Err(PyErr::fetch(obj.py()))
-                        } else {
-                            let val = err_if_invalid_value(obj.py(), -1, ffi::PyLong_AsLong(num));
-                            ffi::Py_DECREF(num);
-                            val
+                let val: c_long;
+                // with python 3.8+ PyLong_AsLong takes care of calling PyNumber_Index itself
+                // hence no need for the slow `PyNumber_Index` path
+                // see https://github.com/PyO3/pyo3/pull/3742 for detials.
+                #[cfg(Py_3_8)]
+                {
+                    val = err_if_invalid_value(obj.py(), -1, unsafe { ffi::PyLong_AsLong(obj.as_ptr()) })?;
+                }
+                #[cfg(not(Py_3_8))]
+                {
+                    val = if let Ok(long) = obj.downcast::<PyLong>() {
+                        // fast path - checking for subclass of `int` just checks a bit in the type object
+                        err_if_invalid_value(obj.py(), -1, unsafe { ffi::PyLong_AsLong(long.as_ptr()) })
+                    } else {
+                        unsafe {
+                            let num = ffi::PyNumber_Index(obj.as_ptr());
+                            if num.is_null() {
+                                Err(PyErr::fetch(obj.py()))
+                            } else {
+                                let val = err_if_invalid_value(obj.py(), -1, ffi::PyLong_AsLong(num));
+                                ffi::Py_DECREF(num);
+                                val
+                            }
                         }
-                    }
-                }?;
+                    }?;
+                }
                 <$rust_type>::try_from(val)
                     .map_err(|e| exceptions::PyOverflowError::new_err(e.to_string()))
             }