py/objstr: Make empty bytes object have a null-terminating byte.

dpgeorge · dpgeorge · commit dfa563c71fea · 2017-10-04T17:59:22.000+11:00
Because a lot of string processing functions assume there is a null terminating byte, so they can work in an efficient way. Fixes issue adafruit#3334.
diff --git a/py/objstr.c b/py/objstr.c
@@ -1973,8 +1973,8 @@ const mp_obj_type_t mp_type_bytes = {
     .locals_dict = (mp_obj_dict_t*)&str8_locals_dict,
 };
 
-// the zero-length bytes
-const mp_obj_str_t mp_const_empty_bytes_obj = {{&mp_type_bytes}, 0, 0, NULL};
+// The zero-length bytes object, with data that includes a null-terminating byte
+const mp_obj_str_t mp_const_empty_bytes_obj = {{&mp_type_bytes}, 0, 0, (const byte*)""};
 
 // Create a str/bytes object using the given data.  New memory is allocated and
 // the data is copied across.
diff --git a/tests/basics/bytes.py b/tests/basics/bytes.py
@@ -8,6 +8,9 @@
 print(bytes())
 print(bytes(b'abc'))
 
+# make sure empty bytes is converted correctly
+print(str(bytes(), 'utf-8'))
+
 a = b"123"
 print(a)
 print(str(a))
