support __signature__ property on CyFunction in Py3.4

Cython/Utility/CythonFunction.c

@@ -70,6 +70,8 @@ static int __Pyx_CyFunction_init(void);
 //////////////////// CythonFunction ////////////////////
 //@substitute: naming
 //@requires: CommonTypes.c::FetchCommonType
+//@requires: ObjectHandling.c::PyObjectCallMethod
+//@requires: ObjectHandling.c::PyObjectGetAttrStr
 
 static PyObject *
 __Pyx_CyFunction_get_doc(__pyx_CyFunctionObject *op, CYTHON_UNUSED void *closure)
@@ -347,6 +349,31 @@ __Pyx_CyFunction_get_annotations(__pyx_CyFunctionObject *op) {
     return result;
 }
 
+#if PY_VERSION_HEX >= 0x030400C1
+static PyObject *
+__Pyx_CyFunction_get_signature(__pyx_CyFunctionObject *op) {
+    PyObject *inspect_module, *signature_class, *signature;
+    // from inspect import Signature
+    inspect_module = PyImport_ImportModuleLevelObject(PYIDENT("inspect"), NULL, NULL, NULL, 0);
+    if (unlikely(!inspect_module))
+        goto bad;
+    signature_class = __Pyx_PyObject_GetAttrStr(inspect_module, PYIDENT("Signature"));
+    Py_DECREF(inspect_module);
+    if (unlikely(!signature_class))
+        goto bad;
+    // return Signature.from_function(op)
+    signature = __Pyx_PyObject_CallMethod1(signature_class, PYIDENT("from_function"), op);
+    Py_DECREF(signature_class);
+    if (likely(signature))
+        return signature;
+bad:
+    // make sure we raise an AttributeError from this property on any errors
+    if (!PyErr_ExceptionMatches(PyExc_AttributeError))
+        PyErr_SetString(PyExc_AttributeError, "failed to calculate __signature__");
+    return NULL;
+}
+#endif
+
 static PyGetSetDef __pyx_CyFunction_getsets[] = {
     {(char *) "func_doc", (getter)__Pyx_CyFunction_get_doc, (setter)__Pyx_CyFunction_set_doc, 0, 0},
     {(char *) "__doc__",  (getter)__Pyx_CyFunction_get_doc, (setter)__Pyx_CyFunction_set_doc, 0, 0},
@@ -366,6 +393,9 @@ static PyGetSetDef __pyx_CyFunction_getsets[] = {
     {(char *) "__defaults__", (getter)__Pyx_CyFunction_get_defaults, (setter)__Pyx_CyFunction_set_defaults, 0, 0},
     {(char *) "__kwdefaults__", (getter)__Pyx_CyFunction_get_kwdefaults, (setter)__Pyx_CyFunction_set_kwdefaults, 0, 0},
     {(char *) "__annotations__", (getter)__Pyx_CyFunction_get_annotations, (setter)__Pyx_CyFunction_set_annotations, 0, 0},
+#if PY_VERSION_HEX >= 0x030400C1
+    {(char *) "__signature__", (getter)__Pyx_CyFunction_get_signature, 0, 0, 0},
+#endif
     {0, 0, 0, 0, 0}
 };
 

tests/run/cyfunction.pyx

@@ -55,6 +55,22 @@ def inspect_signature(a, b, c=123, *, d=234):
     return inspect.signature(inspect_signature) if IS_PY34 else None
 
 
+def test___signature__(a, b, c=123, *, d=234):
+    """
+    >>> sig = test___signature__(1, 2)
+    >>> if IS_PY34: list(sig.parameters)
+    ... else: ['a', 'b', 'c', 'd']
+    ['a', 'b', 'c', 'd']
+    >>> if IS_PY34: sig.parameters['c'].default == 123
+    ... else: True
+    True
+    >>> if IS_PY34: sig.parameters['d'].default == 234
+    ... else: True
+    True
+    """
+    return inspect_signature.__signature__ if IS_PY34 else None
+
+
 def test_dict():
     """
     >>> test_dict.foo = 123