python KeyError:0

Question

My program streaming data from Twython generates this error:

longitude=data['coordinates'][0]
KeyError: 0

This occurs in the following code:

class MyStreamer(TwythonStreamer):
    def on_success(self, data):
        if 'text' in data:
            if data['place']!=None:
                if 'coordinates' in data and data['coordinates'] is not None:
                    longitude=data['coordinates'][0]

I then inserted a print(data['coordinates']) the line before the longitude statement and the most recent time this error intermittently happened it printed out {'coordinates': [-73.971836, 40.798598], 'type': 'Point'} . Though sometimes it reverses the order of key entries like this: {'type': 'Point', 'coordinates': [-73.97189946, 40.79853829]}

I then added print calls for type(data) and type(data['coordinates']) and got dict as the result for both when the error happened.

I also now realize this has only happened (and happens every time) when data['place']!=None . So I am now doing print calls on data['place'] , type(data['place']) and repr(data['place'])

What else can I put in here to trap for the error/figure out what is going on?

If it helps here is the 200 line python file that includes the TwythonStreamer class definition.

Answer 1

Now that you've added more realistic code to your question, it seems obvious where the problem lies. The Twython streamer doesn't always send coordinate data, and it can be None - but when it does send it, the lat/long values may be nested two layers deep .

So the data structure is this:

{
    'coordinates': {
        'coordinates': [-73.971836, 40.798598],
        'type': 'Point'
    },
    ...
}

Which means your code needs to look like this:

class MyStreamer(TwythonStreamer):
    def on_success(self, data):
        if 'text' in data:
            if 'place' in data and data['place'] is not None:
                if 'coordinates' in data and data['coordinates'] is not None:
                    longitude, latitude = data['coordinates']['coordinates']

Or more simply:

class MyStreamer(TwythonStreamer):
    def on_success(self, data):
        if 'text' in data:
            place = data.get('place')
            if place is not None:
                coords = data.get('coordinates')
                if coords is not None:
                    longitude, latitude = coords['coordinates']