diff --git a/src/data_integration_lib.py b/src/data_integration_lib.py
index 876eb1d..d4f974e 100644
--- a/src/data_integration_lib.py
+++ b/src/data_integration_lib.py
@@ -30,19 +30,20 @@ def integrate_data_sources(yaml_config_file_path, log_dir='logs/'):
         except yaml.YAMLError as exc:
             logging.error("Error loading YAML file: %s", exc)
             raise
+    
+    def output_filename(name, date, initials):
+        return f"{name}_{date}_{initials}.h5"
 
-    output_filename = lambda name, datetime, initials: '_'.join([name,datetime,initials])+'.h5'
     exp_campaign_name = config_dict['experiment_name']
     initials = config_dict['user_name']
     input_file_dir = config_dict['input_file_directory']
     output_dir = config_dict['output_file_directory']
-
     select_dir_keywords = config_dict['instrument_datafolder']
-
-    root_metadata = {'project_name' : config_dict['project_name'],
-                    'experiment_name' : config_dict['experiment_name'],
-                    'user_name' : config_dict['user_name'],
-                    }
+    root_metadata = {
+        'project_name' : config_dict['project_name'],
+        'experiment_name' : config_dict['experiment_name'],
+        'user_name' : config_dict['user_name'],
+    }
 
     if config_dict['datetime_steps']: