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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 randomString(length, chrs=None):
 """Produce a string of length random bytes, chosen from chrs."""

    if chrs is None:
        return getBytes(length)
    else:
        n = len(chrs)
        return ''.join([chrs[randrange(n)] for _ in xrange(length)])