builtin property: accept keyword arguments

this allows python code to use property(lambda:..., doc=...) idiom.

named versions for the fget, fset and fdel arguments are left out in the
interest of saving space; they are rarely used and easy to enable when
actually needed.

a test case is included.

py/objproperty.c

@@ -38,28 +38,22 @@ typedef struct _mp_obj_property_t {
 } mp_obj_property_t;
 
 STATIC mp_obj_t property_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
-    mp_arg_check_num(n_args, n_kw, 0, 4, false);
+    enum { ARG_fget, ARG_fset, ARG_fdel, ARG_doc };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_, MP_ARG_OBJ, {.u_rom_obj = mp_const_none} },
+        { MP_QSTR_, MP_ARG_OBJ, {.u_rom_obj = mp_const_none} },
+        { MP_QSTR_, MP_ARG_OBJ, {.u_rom_obj = mp_const_none} },
+        { MP_QSTR_doc, MP_ARG_OBJ, {.u_rom_obj = mp_const_none} },
+    };
+    mp_arg_val_t vals[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all_kw_array(n_args, n_kw, args, MP_ARRAY_SIZE(allowed_args), allowed_args, vals);
 
     mp_obj_property_t *o = m_new_obj(mp_obj_property_t);
     o->base.type = type;
-    if (n_args >= 4) {
-        // doc ignored
-    }
-    if (n_args >= 3) {
-        o->proxy[2] = args[2];
-    } else {
-        o->proxy[2] = mp_const_none;
-    }
-    if (n_args >= 2) {
-        o->proxy[1] = args[1];
-    } else {
-        o->proxy[1] = mp_const_none;
-    }
-    if (n_args >= 1) {
-        o->proxy[0] = args[0];
-    } else {
-        o->proxy[0] = mp_const_none;
-    }
+    o->proxy[0] = vals[ARG_fget].u_obj;
+    o->proxy[1] = vals[ARG_fset].u_obj;
+    o->proxy[2] = vals[ARG_fdel].u_obj;
+    // vals[ARG_doc] is silently discarded
     return MP_OBJ_FROM_PTR(o);
 }
 

py/qstrdefs.h

@@ -570,6 +570,7 @@ Q(property)
 Q(getter)
 Q(setter)
 Q(deleter)
+Q(doc)
 #endif
 
 #if MICROPY_PY_UZLIB

tests/basics/builtin_property.py

@@ -93,3 +93,10 @@ try:
     del d.prop
 except AttributeError:
     print('AttributeError')
+
+# properties take keyword arguments
+class E:
+    p = property(lambda self: 42, doc="This is truth.")
+    # not tested for because the other keyword arguments are not accepted
+    # q = property(fget=lambda self: 21, doc="Half the truth.")
+print(E().p)