diff --git a/Include/internal/pycore_code.h b/Include/internal/pycore_code.h
index 2839b9b7ebe0fb..eced772493ee30 100644
--- a/Include/internal/pycore_code.h
+++ b/Include/internal/pycore_code.h
@@ -561,6 +561,10 @@ extern void _Py_ClearTLBCIndex(_PyThreadStateImpl *tstate);
extern int _Py_ClearUnusedTLBC(PyInterpreterState *interp);
#endif
+
+PyAPI_FUNC(int) _PyCode_ReturnsOnlyNone(PyCodeObject *);
+
+
#ifdef __cplusplus
}
#endif
diff --git a/Include/internal/pycore_opcode_utils.h b/Include/internal/pycore_opcode_utils.h
index b3056e7bb84c69..62af06dc01c125 100644
--- a/Include/internal/pycore_opcode_utils.h
+++ b/Include/internal/pycore_opcode_utils.h
@@ -54,6 +54,9 @@ extern "C" {
(opcode) == RAISE_VARARGS || \
(opcode) == RERAISE)
+#define IS_RETURN_OPCODE(opcode) \
+ (opcode == RETURN_VALUE)
+
/* Flags used in the oparg for MAKE_FUNCTION */
#define MAKE_FUNCTION_DEFAULTS 0x01
diff --git a/Lib/test/test_code.py b/Lib/test/test_code.py
index 2f459a46b5ad70..0c76d38feaae87 100644
--- a/Lib/test/test_code.py
+++ b/Lib/test/test_code.py
@@ -216,6 +216,10 @@
from test.support.bytecode_helper import instructions_with_positions
from opcode import opmap, opname
from _testcapi import code_offset_to_line
+try:
+ import _testinternalcapi
+except ModuleNotFoundError:
+ _testinternalcapi = None
COPY_FREE_VARS = opmap['COPY_FREE_VARS']
@@ -425,6 +429,61 @@ def func():
with self.assertWarns(DeprecationWarning):
func.__code__.co_lnotab
+ @unittest.skipIf(_testinternalcapi is None, '_testinternalcapi is missing')
+ def test_returns_only_none(self):
+ value = True
+
+ def spam1():
+ pass
+ def spam2():
+ return
+ def spam3():
+ return None
+ def spam4():
+ if not value:
+ return
+ ...
+ def spam5():
+ if not value:
+ return None
+ ...
+ lambda1 = (lambda: None)
+ for func in [
+ spam1,
+ spam2,
+ spam3,
+ spam4,
+ spam5,
+ lambda1,
+ ]:
+ with self.subTest(func):
+ res = _testinternalcapi.code_returns_only_none(func.__code__)
+ self.assertTrue(res)
+
+ def spam6():
+ return True
+ def spam7():
+ return value
+ def spam8():
+ if value:
+ return None
+ return True
+ def spam9():
+ if value:
+ return True
+ return None
+ lambda2 = (lambda: True)
+ for func in [
+ spam6,
+ spam7,
+ spam8,
+ spam9,
+ lambda2,
+ ]:
+ with self.subTest(func):
+ res = _testinternalcapi.code_returns_only_none(func.__code__)
+ self.assertFalse(res)
+
def test_invalid_bytecode(self):
def foo():
pass
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 575e55a0e9c45a..643bc90bd4332e 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -945,6 +945,18 @@ iframe_getlasti(PyObject *self, PyObject *frame)
return PyLong_FromLong(PyUnstable_InterpreterFrame_GetLasti(f));
}
+static PyObject *
+code_returns_only_none(PyObject *self, PyObject *arg)
+{
+ if (!PyCode_Check(arg)) {
+ PyErr_SetString(PyExc_TypeError, "argument must be a code object");
+ return NULL;
+ }
+ PyCodeObject *code = (PyCodeObject *)arg;
+ int res = _PyCode_ReturnsOnlyNone(code);
+ return PyBool_FromLong(res);
+}
+
static PyObject *
get_co_framesize(PyObject *self, PyObject *arg)
{
@@ -2030,6 +2042,7 @@ static PyMethodDef module_functions[] = {
{"iframe_getcode", iframe_getcode, METH_O, NULL},
{"iframe_getline", iframe_getline, METH_O, NULL},
{"iframe_getlasti", iframe_getlasti, METH_O, NULL},
+ {"code_returns_only_none", code_returns_only_none, METH_O, NULL},
{"get_co_framesize", get_co_framesize, METH_O, NULL},
{"jit_enabled", jit_enabled, METH_NOARGS, NULL},
#ifdef _Py_TIER2
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index 226c64f717dc82..bf24a4af445356 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -1689,6 +1689,49 @@ PyCode_GetFreevars(PyCodeObject *code)
return _PyCode_GetFreevars(code);
}
+
+/* Here "value" means a non-None value, since a bare return is identical
+ * to returning None explicitly. Likewise a missing return statement
+ * at the end of the function is turned into "return None". */
+int
+_PyCode_ReturnsOnlyNone(PyCodeObject *co)
+{
+ // Look up None in co_consts.
+ Py_ssize_t nconsts = PyTuple_Size(co->co_consts);
+ int none_index = 0;
+ for (; none_index < nconsts; none_index++) {
+ if (PyTuple_GET_ITEM(co->co_consts, none_index) == Py_None) {
+ break;
+ }
+ }
+ if (none_index == nconsts) {
+ // None wasn't there, which means there was no implicit return,
+ // "return", or "return None". That means there must be
+ // an explicit return (non-None).
+ return 0;
+ }
+
+ // Walk the bytecode, looking for RETURN_VALUE.
+ Py_ssize_t len = Py_SIZE(co);
+ for (int i = 0; i < len; i++) {
+ _Py_CODEUNIT inst = _Py_GetBaseCodeUnit(co, i);
+ if (IS_RETURN_OPCODE(inst.op.code)) {
+ assert(i != 0);
+ // Ignore it if it returns None.
+ _Py_CODEUNIT prev = _Py_GetBaseCodeUnit(co, i-1);
+ if (prev.op.code == LOAD_CONST) {
+ // We don't worry about EXTENDED_ARG for now.
+ if (prev.op.arg == none_index) {
+ continue;
+ }
+ }
+ return 0;
+ }
+ }
+ return 1;
+}
+
+
#ifdef _Py_TIER2
static void
diff --git a/Python/flowgraph.c b/Python/flowgraph.c
index a0d5690250cffb..423904672e8b11 100644
--- a/Python/flowgraph.c
+++ b/Python/flowgraph.c
@@ -295,7 +295,7 @@ dump_instr(cfg_instr *i)
static inline int
basicblock_returns(const basicblock *b) {
cfg_instr *last = basicblock_last_instr(b);
- return last && last->i_opcode == RETURN_VALUE;
+ return last && IS_RETURN_OPCODE(last->i_opcode);
}
static void
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