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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def generate_random_string(length=6):
    '''
    Returns a random string of a specified length.

    >>> len(generate_random_string(length=25))
    25

    Test randomness. Try N times and observe no duplicaton
    >>> N = 100
    >>> len(set(generate_random_string(10) for i in range(N))) == N
    True
    '''
    n = int(length / 2 + 1)
    x = binascii.hexlify(os.urandom(n))
    s = x[:length]
    return s.decode('utf-8')