Issue 25483: Add an opcode to make f-string formatting more robust.

1 files changed, 57 insertions, 0 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index f9e8ef8..60db703 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -3363,6 +3363,63 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
             DISPATCH();
         }
 
+        TARGET(FORMAT_VALUE) {
+            /* Handles f-string value formatting. */
+            PyObject *result;
+            PyObject *fmt_spec;
+            PyObject *value;
+            PyObject *(*conv_fn)(PyObject *);
+            int which_conversion = oparg & FVC_MASK;
+            int have_fmt_spec = (oparg & FVS_MASK) == FVS_HAVE_SPEC;
+
+            fmt_spec = have_fmt_spec ? POP() : NULL;
+            value = TOP();
+
+            /* See if any conversion is specified. */
+            switch (which_conversion) {
+            case FVC_STR:   conv_fn = PyObject_Str;   break;
+            case FVC_REPR:  conv_fn = PyObject_Repr;  break;
+            case FVC_ASCII: conv_fn = PyObject_ASCII; break;
+
+            /* Must be 0 (meaning no conversion), since only four
+               values are allowed by (oparg & FVC_MASK). */
+            default:        conv_fn = NULL;           break;
+            }
+
+            /* If there's a conversion function, call it and replace
+               value with that result. Otherwise, just use value,
+               without conversion. */
+            if (conv_fn) {
+                result = conv_fn(value);
+                Py_DECREF(value);
+                if (!result) {
+                    Py_XDECREF(fmt_spec);
+                    goto error;
+                }
+                value = result;
+            }
+
+            /* If value is a unicode object, and there's no fmt_spec,
+               then we know the result of format(value) is value
+               itself. In that case, skip calling format(). I plan to
+               move this optimization in to PyObject_Format()
+               itself. */
+            if (PyUnicode_CheckExact(value) && fmt_spec == NULL) {
+                /* Do nothing, just transfer ownership to result. */
+                result = value;
+            } else {
+                /* Actually call format(). */
+                result = PyObject_Format(value, fmt_spec);
+                Py_DECREF(value);
+                Py_XDECREF(fmt_spec);
+                if (!result)
+                    goto error;
+            }
+
+            SET_TOP(result);
+            DISPATCH();
+        }
+
         TARGET(EXTENDED_ARG) {
             opcode = NEXTOP();
             oparg = oparg<<16 | NEXTARG();