Twitter流：尝试/除外IndexError

Question

Background: I want to download specific parts of users tweets (eg username, id, expanded url, etc) from the twitter api. I am able to do so successfully.

Problem: Because not all users have expanded_url , I sometimes receive the following error:

IndexError: list index out of range

Goal: If such IndexError occur, skip and proceed to collect new tweets

I think one way to solve this problem is by using a try/except statement

Questions: Is a try/except statement a valid way to do achieve this goal? If so, how do I properly apply a try/except statement?

I have tried the following:

class StdOutListener(StreamListener):
         def on_data(self, data):
             t = json.loads(data)
             tweet_id = t['id_str'] 
             user_name = t['user']['name'] 
             try:
                 expanded_url = t['entities']['urls'][0]['expanded_url']
             except:
                 pass 

But I get the following error:

UnboundLocalError: local variable 'expanded_url' referenced before assignment

I have searched around SO, and have a few examples similar to my question ( UnboundLocalError: local variable 'url_request' referenced before assignment , UnboundLocalError: local variable 'url' referenced before assignment )

But I'm not sure how to directly change my code so that I can implement the try/except statement. I am also open to other ways to solve this problem. Thank you!

Answer 1

When the block inside the try has an error, the block inside the except gets executed. If nothing happens in your except (it only passes) expanded_url is never defined. You should assign expanded_url inside the except block to a default value or empty strings, whatever it should be:

         try:
             expanded_url = t['entities']['urls'][0]['expanded_url']
         except:
             expanded_url = ''

Answer 2

The problem is that you are probably trying to use the expanded_url after the try/except block but when your code throws the exception you don't create the variable. Try to either:

expanded_url = ''
try:
    expanded_url = ....
except:
    pass

Or:

try:
    expanded_url = ....
except:
    expanded_url = ''