bpo-40521: Make empty Unicode string per interpreter (GH-21096)
Each interpreter now has its own empty Unicode string singleton.
diff --git a/Objects/stringlib/partition.h b/Objects/stringlib/partition.h
index 3731df5..bcc2176 100644
--- a/Objects/stringlib/partition.h
+++ b/Objects/stringlib/partition.h
@@ -1,9 +1,14 @@
/* stringlib: partition implementation */
#ifndef STRINGLIB_FASTSEARCH_H
-#error must include "stringlib/fastsearch.h" before including this module
+# error must include "stringlib/fastsearch.h" before including this module
#endif
+#if !STRINGLIB_MUTABLE && !defined(STRINGLIB_GET_EMPTY)
+# error "STRINGLIB_GET_EMPTY must be defined if STRINGLIB_MUTABLE is zero"
+#endif
+
+
Py_LOCAL_INLINE(PyObject*)
STRINGLIB(partition)(PyObject* str_obj,
const STRINGLIB_CHAR* str, Py_ssize_t str_len,