add pre_process

django_diu/import_command.py

@@ -76,6 +76,9 @@ class ImportTask(object):
     def post_process(self):
         pass
 
+    def pre_process(self):
+        pass
+
     def _process_rows(self, rows, progress=None):
         for row in rows:
             try:
@@ -105,6 +108,7 @@ class ImportTask(object):
     def _run_import_loop(self):
         self.open_data_source()
         self.count_source()
+        self.pre_process()
         if self.progress_bar is True:
             with click.progressbar(length=self.source_count,
                                 label='Importing ' + self.description + ' (' + str(self.source_count) + ' rows to process).') as progress: