py: Add mp_errno_to_str() and use it to provide nicer OSError msgs.

If an OSError is raised with an integer argument, and that integer
corresponds to an errno, then the string for the errno is used as the
argument to the exception, instead of the integer.  Only works if
the uerrno module is enabled.

1 files changed, 9 insertions, 0 deletions

diff --git a/py/moduerrno.c b/py/moduerrno.c
index 826f52d2e..0b543a193 100644
--- a/py/moduerrno.c
+++ b/py/moduerrno.c
@@ -89,4 +89,13 @@ const mp_obj_module_t mp_module_uerrno = {
     .globals = (mp_obj_dict_t*)&mp_module_uerrno_globals,
 };
 
+mp_obj_t mp_errno_to_str(mp_obj_t errno_val) {
+    mp_map_elem_t *elem = mp_map_lookup((mp_map_t*)&errorcode_dict.map, errno_val, MP_MAP_LOOKUP);
+    if (elem == NULL) {
+        return errno_val;
+    } else {
+        return elem->value;
+    }
+}
+
 #endif //MICROPY_PY_UERRNO