Python simple ngrams

ngrams.py

def multigrams(text, lower, upper):
    grams = []
    for i in range(lower, upper):
        grams.extend(ngrams(text, i))
    return grams

def multigrams_count(text, lower, upper):
    counted_grams = {}
    for n in multigrams(text, lower, upper):
        try:
            if " ".join(map(str,n)) in counted_grams:
                counted_grams[" ".join(map(str,n))] = counted_grams[" ".join(map(str,n))] + 1
            else:
                counted_grams[" ".join(map(str,n))] = 1
        except:
            pass
    return counted_grams

def multigrams_sort_filter(text, lowern, uppern, threshold):
    counted_grams = multigrams_count(text,lowern,uppern)
    filtered_grams = {k : v for k,v in counted_grams.iteritems() if v >= threshold}
    return sorted(filtered_grams.iteritems(), key=operator.itemgetter(1))