input: Write a python function to extract all routes from a Flask app.
  assert extract_routes(app) == ['/', '/data', '/data/int:id']
  assert extract_routes(another_app) == ['/home', '/about', '/contact']
  assert extract_routes(empty_app) == []
output: def extract_routes(app):
      routes = []
      for rule in app.url_map.iter_rules():
          routes.append(str(rule))
      return routes