def _get_full_text(tweet):
    """
    Parses a tweet json to retrieve the full text.
    
    :input tweet: a nested dictionary of a Tweet either from the streaming or search API.
    :returns: string of the full_text field hidden in the Tweet
    """
    if isinstance(tweet, dict):
        if 'extended_tweet' in tweet and 'full_text' in tweet['extended_tweet'
            ]:
            return tweet['extended_tweet']['full_text']
        elif 'full_text' in tweet:
            tweet['full_text']
        else:
            return tweet.get('text')
    else:
        dtype = type(tweet)
        raise ValueError('Input needs to be key-value pair! Input is {}'.
            format(dtype))
