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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 _gcd(a, b):
 """Calculate the Greatest Common Divisor of a and b. Unless b==0, the result will have the same sign as b (so that when b is divided by it, the result comes out positive). """

    while b:
        a, b = b, (a % b)
    return a