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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 newpin(digits=4):
 """ Return a random numeric string with the specified number of digits, default 4. 4 5 True """

    randnum = randint(0, 10 ** digits)
    while len(str(randnum)) > digits:
        randnum = randint(0, 10 ** digits)
    return (u'%%0%dd' % digits) % randnum