human
Complete this python program:
def dice_coefficient(string1, string2):
assistant
#Here is the Python program you requested.

    """Returns the similarity between string1 and string1 as a number between 0.0 and 1.0,
    based on the number of shared bigrams, e.g., "night" and "nacht" have one common bigram "ht".
    """
    def bigrams(s):
        return set((s[i:(i + 2)] for i in xrange((len(s) - 1))))
    nx = bigrams(string1)
    ny = bigrams(string2)
    nt = nx.intersection(ny)
    return ((2.0 * len(nt)) / ((len(nx) + len(ny)) or 1))