Fix cnfvar case of writing bytes from the io module

diff --git a/src/cnfvar.py b/src/cnfvar.py
index a05fe0e..5999ba6 100644 (file)
--- a/src/cnfvar.py
+++ b/src/cnfvar.py
@@ -749,7 +749,7 @@ def dump_cnf_string(root, renumber=False):
     string.
     """
     cnf = cnf_root(root)
-    out = io.StringIO()
+    out = io.BytesIO()
     output_cnf(root, out, renumber=renumber, bytes=False)
     res = out.getvalue()
     out.close()