Check bytes exact first to speed up that case

from_bytes_flags: Mean +- std dev: [main] 28.3 ns +- 1.3 ns -> [exactbytes] 27.3 ns +- 0.3 ns: 1.04x faster
bench_convert[bytearray]: Mean +- std dev: [main] 65.8 ns +- 3.3 ns -> [exactbytes] 53.1 ns +- 5.1 ns: 1.24x faster
bench_convert_big[bytes]: Mean +- std dev: [main] 51.8 ns +- 0.6 ns -> [exactbytes] 50.3 ns +- 0.5 ns: 1.03x faster
bench_convert_big[bytearray]: Mean +- std dev: [main] 65.8 ns +- 3.0 ns -> [exactbytes] 53.5 ns +- 5.3 ns: 1.23x faster

Benchmark hidden because not significant (1): bench_convert[bytes]

Author: cmaloney

Misc/NEWS.d/next/Core_and_Builtins/2025-04-04-20-38-29.gh-issue-132108.UwZIQy.rst

@@ -1,2 +1,2 @@
 Speed up :meth:`int.from_bytes` when passed object supports :ref:`buffer
-protocol <bufferobjects>`, like :class:`bytearray`.
+protocol <bufferobjects>`, like :class:`bytearray` by ~1.2x.

Objects/longobject.c

@@ -6454,7 +6454,11 @@ int_from_bytes_impl(PyTypeObject *type, PyObject *bytes_obj,
     }
 
     /* Use buffer protocol to avoid copies. */
-    if (PyObject_CheckBuffer(bytes_obj)) {
+    if (PyBytes_CheckExact(bytes_obj)) {
+        long_obj = _PyLong_FromByteArray(
+            (unsigned char *)PyBytes_AS_STRING(bytes_obj), Py_SIZE(bytes_obj),
+            little_endian, is_signed);
+    } else if (PyObject_CheckBuffer(bytes_obj)) {
         if (PyObject_GetBuffer(bytes_obj, &view, PyBUF_SIMPLE) != 0) {
             return NULL;
         }