lib/parser: Use None as default for overwrite (#6076)

Use None, not False, as a default value for overwrite, verbose etc. None is more appropriate because the default behavior is influenced by the environment and, very generally, by how the library is set up. While False is correct in terms of the corresponding command line not being set, the False value may create a false perception that overwriting will be disabled, but in fact overwriting will be driven by the environment.

Author: wenzeslaus

lib/gis/parser_md_python.c

@@ -76,7 +76,8 @@ void print_python_long_flag(FILE *file, const char *key, const char *label,
     }
     fprintf(file, "%s", indent);
     G__md_print_escaped(file, "\t");
-    fprintf(file, "Default: *False*");
+    const char *flag_default = "*None*";
+    fprintf(file, "Default: %s", flag_default);
 }
 
 void print_python_tuple(FILE *file, const char *type, int num_items)
@@ -436,12 +437,13 @@ void G__md_print_python_short_version(FILE *file, const char *indent)
         fprintf(file, "%s    **flags**=*None*,\n", indent);
     }
 
+    const char *flag_default = "*None*";
     if (new_prompt)
-        fprintf(file, "%s    **overwrite**=*False*,\n", indent);
+        fprintf(file, "%s    **overwrite**=%s,\n", indent, flag_default);
 
-    fprintf(file, "%s    **verbose**=*False*,\n", indent);
-    fprintf(file, "%s    **quiet**=*False*,\n", indent);
-    fprintf(file, "%s    **superquiet**=*False*)\n", indent);
+    fprintf(file, "%s    **verbose**=%s,\n", indent, flag_default);
+    fprintf(file, "%s    **quiet**=%s,\n", indent, flag_default);
+    fprintf(file, "%s    **superquiet**=%s)\n", indent, flag_default);
 
     print_python_example(file, python_function, output_format_default, indent);
 }