py/objmodule: Implement PEP 562's __getattr__ for modules.

Configurable via MICROPY_MODULE_GETATTR, disabled by default.  Among other
things __getattr__ for modules can help to build lazy loading / code
unloading at runtime.

ports/unix/mpconfigport_coverage.h

@@ -36,6 +36,7 @@
 #define MICROPY_FLOAT_HIGH_QUALITY_HASH (1)
 #define MICROPY_ENABLE_SCHEDULER       (1)
 #define MICROPY_READER_VFS             (1)
+#define MICROPY_MODULE_GETATTR         (1)
 #define MICROPY_PY_DELATTR_SETATTR     (1)
 #define MICROPY_PY_REVERSE_SPECIAL_METHODS (1)
 #define MICROPY_PY_BUILTINS_RANGE_BINOP (1)

py/mpconfig.h

@@ -633,6 +633,11 @@ typedef double mp_float_t;
 #define MICROPY_MODULE_BUILTIN_INIT (0)
 #endif
 
+// Whether to support module-level __getattr__ (see PEP 562)
+#ifndef MICROPY_MODULE_GETATTR
+#define MICROPY_MODULE_GETATTR (0)
+#endif
+
 // Whether module weak links are supported
 #ifndef MICROPY_MODULE_WEAK_LINKS
 #define MICROPY_MODULE_WEAK_LINKS (0)

py/objmodule.c

@@ -61,6 +61,13 @@ STATIC void module_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
         mp_map_elem_t *elem = mp_map_lookup(&self->globals->map, MP_OBJ_NEW_QSTR(attr), MP_MAP_LOOKUP);
         if (elem != NULL) {
             dest[0] = elem->value;
+        #if MICROPY_MODULE_GETATTR
+        } else if (attr != MP_QSTR___getattr__) {
+            elem = mp_map_lookup(&self->globals->map, MP_OBJ_NEW_QSTR(MP_QSTR___getattr__), MP_MAP_LOOKUP);
+            if (elem != NULL) {
+                dest[0] = mp_call_function_1(elem->value, MP_OBJ_NEW_QSTR(attr));
+            }
+        #endif
         }
     } else {
         // delete/store attribute

tests/import/module_getattr.py

@@ -0,0 +1,23 @@
+# test __getattr__ on module
+
+# ensure that does_not_exist doesn't exist to start with
+this = __import__(__name__)
+try:
+    this.does_not_exist
+    assert False
+except AttributeError:
+    pass
+
+# define __getattr__
+def __getattr__(attr):
+    if attr == 'does_not_exist':
+        return False
+    raise AttributeError
+
+# do feature test (will also test functionality if the feature exists)
+if not hasattr(this, 'does_not_exist'):
+    print('SKIP')
+    raise SystemExit
+
+# check that __getattr__ works as expected
+print(this.does_not_exist)