diff --git a/thirdparty/train_api.py b/thirdparty/train_api.py
index e881c5a..ca6c2ae 100644
--- a/thirdparty/train_api.py
+++ b/thirdparty/train_api.py
@@ -44,7 +44,9 @@ class TrainServer(BaseHTTPRequestHandler):
 
         # Helper to format datetime
         def format_datetime(year, month, day, hour, minute):
-            return f"{year:04d}-{month:02d}-{day:02d}T{hour:02d}:{minute:02d}"
+            return "{year:04d}-{month:02d}-{day:02d}T{hour:02d}:{minute:02d}".format(
+                year=year, month=month, day=day, hour=hour, minute=minute
+            )
 
         # Generate outbound journeys
         year, month, day, hour, minute = out_datetime
@@ -66,7 +68,7 @@ class TrainServer(BaseHTTPRequestHandler):
             arr_hour = arr_hour % 24
 
             journey = {
-                "id": f"T{random.randint(1000, 9999)}",
+                "id": "T%s".format(random.randint(1000, 9999)),
                 "type": "outbound",
                 "departure": origin,
                 "arrival": destination,
@@ -99,7 +101,7 @@ class TrainServer(BaseHTTPRequestHandler):
                 arr_hour = arr_hour % 24
 
                 journey = {
-                    "id": f"T{random.randint(1000, 9999)}",
+                    "id": "T%s".format(random.randint(1000, 9999)),
                     "type": "return",
                     "departure": destination,
                     "arrival": origin,