"""
Ex 7.25 from A Primer on ...
Add __sub__ special method to polynomial class
"""

class Polynomial:
    def __init__(self, coefficients):
        self.coeff = coefficients

    def __call__(self, x):
        """Evaluate the polynomial."""
        s = 0
        for i in range(len(self.coeff)):
            s += self.coeff[i]*x**i
        return s

    def __add__(self, other):
        """Return self + other as Polynomial object."""
        # Two cases:
        #
        # self: X X X X X X X
        #other: X X X
        #
        # or:
        #
        # self: X X X
        #other: X X X X X X X

        # Start with the longest list and add in the other
        if len(self.coeff) > len(other.coeff):
            result_coeff = self.coeff[:]  # copy!
            for i in range(len(other.coeff)):
                result_coeff[i] += other.coeff[i]
        else:
            result_coeff = other.coeff[:] # copy!
            for i in range(len(self.coeff)):
                result_coeff[i] += self.coeff[i]
        return Polynomial(result_coeff)

    def __sub__(self,other):
        if len(self.coeff) > len(other.coeff):
            result_coeff = self.coeff[:]  # copy!
            for i in range(len(other.coeff)):
                result_coeff[i] -= other.coeff[i]
        else:
            result_coeff = [0]*len(other.coeff)
            for i in range(len(self.coeff)):
                result_coeff[i] = self.coeff[i]
            for i in range(len(other.coeff)):
                result_coeff[i] -= other.coeff[i]

        return Polynomial(result_coeff)


p1 = Polynomial([1,1,1,1])  #1 + x + x**2 + x**3
p2 = Polynomial([0,1,2])    #x + 2*x**2

print(p1(0.5)) # = 1.875
print(p2(0.5)) # = 1.0

p3 = p1+p2      #= 1+2*x+3*x**2 +x**3
print(p3(1.0))  # = 7.0

p4 = p1-p2

print(p4(1.0))

"""
Terminal> python Polynomial_sub.py
1.875
1.0
7.0
1.0
"""