py/objfun: Support fun.__globals__ attribute.

This returns a reference to the globals dict associated with the function,
ie the global scope that the function was defined in.  This attribute is
read-only but the dict itself is modifiable, per CPython behaviour.

Signed-off-by: Damien George <damien@micropython.org>

py/objfun.c

@@ -355,6 +355,10 @@ void mp_obj_fun_bc_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
     if (attr == MP_QSTR___name__) {
         dest[0] = MP_OBJ_NEW_QSTR(mp_obj_fun_get_name(self_in));
     }
+    if (attr == MP_QSTR___globals__) {
+        mp_obj_fun_bc_t *self = MP_OBJ_TO_PTR(self_in);
+        dest[0] = MP_OBJ_FROM_PTR(self->globals);
+    }
 }
 #endif
 

tests/basics/fun_globals.py

@@ -0,0 +1,21 @@
+# test the __globals__ attribute of a function
+
+
+def foo():
+    pass
+
+
+if not hasattr(foo, "__globals__"):
+    print("SKIP")
+    raise SystemExit
+
+print(type(foo.__globals__))
+print(foo.__globals__ is globals())
+
+foo.__globals__["bar"] = 123
+print(bar)
+
+try:
+    foo.__globals__ = None
+except AttributeError:
+    print("AttributeError")