You can get unique values by converting the list to a set first:
your_list = [u'hello', u'how', u'how', u'is', u'your', u'life', u'going']
your_set = set(your_list)
You may covert the set to a list later using your_newlist = list(your_set) in the above code.
Similarly, if you start with a set instead of a list use this code to get unique values:
output = set()
for x in trends:
But remember, sets do not maintain the original order. To know more about the set order visit here:http://code.activestate.com/recipes/576694/