def SquareRoot (N):
    Guess = N / 2.0
    Quotient = N / Guess
    NewGuess = (Guess + Quotient) / 2.0

    while (abs(Guess - NewGuess) > 1.0e-15):
        #print (Guess, NewGuess)
        Guess = NewGuess
        Quotient = N / Guess
        NewGuess = (Guess + Quotient) / 2.0

    return NewGuess

def Distance (X1,Y1,X2=0,Y2=0): # Note that X2 and Y2 now have default values
    A = X2 - X1
    B = Y2 - Y1
    return SquareRoot(A*A + B*B)

print (Distance(3,4,9,12))      # Distance between points <3,4> and <9,12>
print (Distance(3,4))           # Distance between points <3,4> and <0,0>

def Taxes (Gross=50000,Children=0,TaxRate=0.05):
    return Gross * TaxRate / (Children+1)

print (Taxes(65000,3,0.06))     # Filling in all three parameters
print (Taxes(65000,3))          # Filling in first two, third uses default
print (Taxes(65000))            # Filling in first, second two use defaults
print (Taxes())                 # All three parameters use default values