Update app.py

app.py

@@ -225,7 +225,7 @@ def block_users(client, threshold, dataset):
     :return: The number of blocked users.
     '''
     num_users_blocked = 0
-
+    global dropdown
     print("Testing dropdown value {}".format(dropdown.value))
 
     for filename in os.listdir("users"):
@@ -378,6 +378,7 @@ def get_target_website():
 
 # The main chunk of code that uses Gradio blocks to create the UI
 html_button = None
+dropdown = None
 with block:
     gr.HTML('''
 <meta name="viewport" content="width=device-width, initial-scale=1">