“SyntaxWarning: name ‘our_mongo’ is used prior to global declaration”

My code keeps giving me the above syntax warning. My code includes, but is not limited to:

class SocketHandler(WebSocketHandler):
    def on_message(self, message):
        ball = json.loads(message)
        user = User(ball['identifier'])
        if ball['command'] == 'search':
            global our_mongo
            search_results = our_mongo.find({'$text':{'$search':ball['search_term']}},{'score':{'$meta':"textScore"}})
            self.write_message({
                    'command': 'search-results',
                    'results': list(search_results.sort([('score', {'$meta': 'textScore'})]).limit(10)),
            })
        elif ball['command'] == 'save-node': # hopefully this can handle both new nodes and changes to nodes
            node_dict = ball['node_dict']
            if 'importance' in node_dict.keys():
                node_dict['importance'] = int(node_dict['importance'])
            try:
                node_obj = node.create_appropriate_node(node_dict)
                print('node made.  looks like: '+str(node_obj)+'.  Now time to put it into the DB...')
                global our_mongo
                # take a look at the dependencies now
                previous_dependency_ids = [node.reduce_string(dependency) for dependency in list(our_mongo.find({"_id": node_obj.id}))[0]["_dependencies"]] # if this works, try using set() instead of list and elimination the set()s below
                print('prev deps are: '+str(previous_dependency_ids))
                our_mongo.upsert({ "_id": node_obj.id }, node_obj.__dict__)
                # take a look at the current dependencies
                current_dependency_ids = [node.reduce_string(dependency) for dependency in list(our_mongo.find({"_id": node_obj.id}))[0]["_dependencies"]] # if this works, try using set() instead of list and elimination the set()s below
                print('curr deps are: '+str(current_dependency_ids))
                update_our_DAG()
                # send an update of the graph to the user if there is a new dependency:
                for new_dependency in set(current_dependency_ids) - set(previous_dependency_ids):
                    self.request_node(new_dependency, ball, user)
                # OR IF THE SAVED NODE IS A BRAND NEW NODE, we have to include all the deps
            except Exception as error:
                # stuff didn't work, send error back to user
                print('ERROR: '+str(error))
                self.write_message({
                    'command': 'display-error',
                    'message': str(error),
                })


def update_our_DAG():
    # 1. grab nodes and edges from database
    all_node_dicts = list(Mongo("math", "nodes").find())

    # 2. create a networkx graph with the info...
    global our_DAG
    our_DAG = nx.DAG()
    for node_dict in all_node_dicts:
        node = create_appropriate_node(strip_underscores(node_dict))
        our_DAG.add_n(node)

def make_app():
    return Application(
        [
            url('/', RedirectHandler, {"url": "index.html"}, name="rooth"),
            url('/websocket', SocketHandler),
            url('/json', JSONHandler, name="jsonh"),
            url(r'/index(?:.html)?', IndexHandler, name="indexh"),
            # captures anything at all, and serves it as a static file. simple!
            url(r'/(.*)', StaticHandler, {"path": "../www/"}),
        ],
        # settings:
        debug=True,
    )

def make_app_and_start_listening():
    # enable_pretty_logging()
    application = make_app()
    # by listening on the http port (default for all browsers that i know of),
    # user will not have to type "http://" or ":80" in the URL
    application.listen(80)
    # other stuff
    IOLoop.current().start()


if __name__ == "__main__":
    # 0. create a global mongo object for later use (for upserts in the future)
    our_mongo = Mongo("math", "nodes")

    # 1 and 2
    update_our_DAG()

    axioms = [our_DAG.n(node_id) for node_id in ['set', 'multiset', 'vertex']]

    # 3. launch!
    make_app_and_start_listening()

I’ve tried everything and it’s still an issue. WHY is this a syntax error? What is the best way to fix this?

Answer

It is not a SyntaxError but a SyntaxWarning. Python warns that you’re using our_mongo variable before a global our_mongo within the function. Syntactically it does not actually matter on which line of the function the global statement is; but the idiomatic way would be to use global before the first access.

Another issue altogether is that you have multiple global our_mongo statements, where single would do, and also that you do not even need the global at all – it is only for the case when you want to assign a new value to the global variable; i.e.

def foo():
    global bar        # this line is required for the next line 
                      # to change the global variable instead of
                      # the local variable
    bar = 42

Thus, just remove all global statements altogether from your on_message, they’re unnecessary.

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Answer