How to write Flask decorator with request?

It's kind of an old post, but I think that it may benefit from a little correction: decorated_function needs to return f(*args, **kws)

def validate_request(f):
  @functools.wraps(f)
  def decorated_function(*args, **kws):
    # Do something with your request here
    data = flask.request.get_json()
    if not data:
      flask.abort(404)
    return f(*args, **kws)
  return decorated_function

Otherwise you will encounter TypeError: The view function did not return a valid response. The function either returned None or ended without a return statement.

This is how your decorator should look like

def validate_request(f):
  @functools.wraps(f)
  def decorated_function(*args, **kwargs):
    # Do something with your request here
    data = flask.request.get_json()
    if not data:
      flask.abort(404)
    return f(*args, **kwargs)
  return decorated_function

and you will call it like this

@app.route('/todo/api/v1.0/tasks/<int:task_id>', methods=['PUT'])
@validate_request
def update_task(task_id):
    # The rest of your code..