diff --git a/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/app.py b/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/app.py
index fad9141a9..84b52615a 100644
--- a/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/app.py
+++ b/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/app.py
@@ -2,7 +2,7 @@ from flask import Flask, jsonify
 from flask_cors import CORS
 
 import time
-from utils import load_historical_data 
+from utils import load_historical_data
 
 app = Flask(__name__)
 CORS(app)
@@ -11,21 +11,24 @@ start_time = time.time()
 
 historical_data = load_historical_data()
 
+
 @app.route('/exchange_rate/<symbol>')
 def get_stock_data(symbol):
     if symbol not in list(historical_data.keys()):
         return jsonify("Invalid symbol")
     current_time = time.time()
-    step = (int(current_time * 10) - int(start_time * 10)) % len(historical_data[symbol])
+    step = (int(current_time * 10) - int(start_time * 10)
+            ) % len(historical_data[symbol])
     try:
         return jsonify({
             'symbol': 'USD',
             'rate': float(historical_data[symbol][step]),
             'timestamp': current_time
-            })
+        })
     except:
         return "Server Error"
 
+
 @app.route('/stocks_list')
 def list_symbols():
     return jsonify(list(historical_data.keys()))
diff --git a/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/utils.py b/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/utils.py
index d05efc0ed..67acc76c0 100644
--- a/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/utils.py
+++ b/subjects/mobile-dev/stock-market/resources/mock-stock-data-server/utils.py
@@ -5,7 +5,8 @@ import csv
 def load_historical_data(directory_path='./sample-stocks/'):
     historical_data = {}
 
-    file_list = [filename for filename in os.listdir(directory_path) if filename.endswith(".csv")]
+    file_list = [filename for filename in os.listdir(
+        directory_path) if filename.endswith(".csv")]
     for filename in file_list:
         symbol = filename.replace(".csv", "")
 
@@ -21,4 +22,3 @@ def load_historical_data(directory_path='./sample-stocks/'):
 if __name__ == "__main__":
     result = load_historical_data()
     print(f'keys: {result.keys()}')
-