Issue #9422: Fix memory leak when re-initializing a struct.Struct object.

Misc/NEWS

@@ -1492,6 +1492,8 @@ Library
 Extension Modules
 -----------------
 
+- Issue #9422: Fix memory leak when re-initializing a struct.Struct object.
+
 - Issue #7900: The getgroups(2) system call on MacOSX behaves rather oddly
   compared to other unix systems. In particular, os.getgroups() does
   not reflect any changes made using os.setgroups() but basicly always

Modules/_struct.c

@@ -1247,6 +1247,9 @@ prepare_s(PyStructObject *self)
         PyErr_NoMemory();
         return -1;
     }
+    /* Free any s_codes value left over from a previous initialization. */
+    if (self->s_codes != NULL)
+        PyMem_FREE(self->s_codes);
     self->s_codes = codes;
 
     s = fmt;