Issue #27078: Added BUILD_STRING opcode. Optimized f-strings evaluation.

1 files changed, 19 insertions, 1 deletions

diff --git a/Objects/abstract.c b/Objects/abstract.c
index 654fc0295b..d876dc5fe4 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -675,13 +675,31 @@ PyObject_Format(PyObject *obj, PyObject *format_spec)
     PyObject *result = NULL;
     _Py_IDENTIFIER(__format__);
 
+    if (format_spec != NULL && !PyUnicode_Check(format_spec)) {
+        PyErr_Format(PyExc_SystemError,
+                     "Format specifier must be a string, not %.200s",
+                     Py_TYPE(format_spec)->tp_name);
+        return NULL;
+    }
+
+    /* Fast path for common types. */
+    if (format_spec == NULL || PyUnicode_GET_LENGTH(format_spec) == 0) {
+        if (PyUnicode_CheckExact(obj)) {
+            Py_INCREF(obj);
+            return obj;
+        }
+        if (PyLong_CheckExact(obj)) {
+            return PyObject_Str(obj);
+        }
+    }
+
     /* If no format_spec is provided, use an empty string */
     if (format_spec == NULL) {
         empty = PyUnicode_New(0, 0);
         format_spec = empty;
     }
 
-    /* Find the (unbound!) __format__ method (a borrowed reference) */
+    /* Find the (unbound!) __format__ method */
     meth = _PyObject_LookupSpecial(obj, &PyId___format__);
     if (meth == NULL) {
         if (!PyErr_Occurred())