Update app.py

app.py

@@ -332,7 +332,8 @@ def generate_certificate(certificate_model, first_name, last_name):
 def add_certified_user(hf_username, first_name, last_name, pass_percentage):
   repo.git_pull()
   history = pd.read_csv(os.path.join(CERTIFIED_USERS_DIR, CERTIFIED_USERS_FILENAME))
-  check = history.query('hf_username ==' + str(hf_username))
+  query = 'hf_username ==' + hf_username
+  check = history.query(query)
   print("CHECK", check)
   print("INDEX", check.index)
   new_row = pd.DataFrame({'hf_username': hf_username, 'first_name': first_name, 'last_name': last_name, 'pass_percentage': pass_percentage, 'datetime': time.time()}, index=[0])