diff --git a/volia/core/data.py b/volia/core/data.py
index 6861f2b..8b8383b 100644
--- a/volia/core/data.py
+++ b/volia/core/data.py
@@ -127,7 +127,10 @@ def write_line(id_, values=[], out=sys.stdout):
         values (list, optional): list of values to write, features or labels. Defaults to [].
         out (_io.TextIOWrapper, optional): . Defaults to sys.stdout.
     """
-    if len(values) == 0:
-        out.write(str(id_) + "\n")
+    if hasattr(values, '__len__'):
+        if len(values) == 0:
+            out.write(str(id_) + "\n")
+        else:
+            out.write(str(id_) + " " + " ".join(values) + "\n")
     else:
-        out.write(str(id_) + " " + " ".join(values) + "\n")
\ No newline at end of file
+        out.write(str(id_) + " " + str(values) + "\n")
\ No newline at end of file