Implement PEP 3131. Add isidentifier to str.
diff --git a/Lib/test/badsyntax_3131.py b/Lib/test/badsyntax_3131.py
new file mode 100644
index 0000000..901d374
--- /dev/null
+++ b/Lib/test/badsyntax_3131.py
@@ -0,0 +1,2 @@
+# -*- coding: utf-8 -*-
+€ = 2