Add more debug prints.

Author: serhiy-storchaka

Python/_warnings.c

@@ -1457,10 +1457,14 @@ PyErr_WarnExplicitObject(PyObject *category, PyObject *message,
     if (tstate == NULL) {
         return -1;
     }
+    if (filename)
+        PySys_FormatStdout("filename = %R\n", filename);
+    else
+        PySys_FormatStdout("filename = NULL\n");
     if (module)
         PySys_FormatStdout("module = %R\n", module);
-    // else
-    //     PySys_FormatStdout("module = NULL\n");
+    else
+        PySys_FormatStdout("module = NULL\n");
 
     warnings_lock(tstate->interp);
     res = warn_explicit(tstate, category, message, filename, lineno,