polynomial.py

from itertools import zip_longest


# strip all copies of elt from the end of the list
def strip(L, elt):
   if len(L) == 0: return L

   i = len(L) - 1
   while i >= 0 and L[i] == elt:
      i -= 1

   return L[:i+1]


class Polynomial(object):
   def __init__(self, coefficients):
      self.coefficients = strip(coefficients, 0)
      self.indeterminate = 'x'

   def add(self, other):
      newCoefficients = [sum(x) for x in zip_longest(self, other, fillvalue=0)]
      return Polynomial(newCoefficients)

   def __add__(self, other):
      return  self.add(other)

   def multiply(self, other):
      newCoeffs = [0] * (len(self) + len(other) - 1)

      for i,a in enumerate(self):
         for j,b in enumerate(other):
            newCoeffs[i+j] += a*b

      return Polynomial(strip(newCoeffs, 0))

   def __mul__(self, other):
      return self.multiply(other)

   def __len__(self):
      return len(self.coefficients)

   def __repr__(self):
      return ' + '.join(['%s %s^%d' % (a, self.indeterminate, i) if i > 0 else '%s'%a
                           for i,a in enumerate(self.coefficients)])

   def evaluateAt(self, x):
      theSum = 0

      for c in reversed(self.coefficients):
         theSum = theSum * x + c

      return theSum


   def __iter__(self): return iter(self.coefficients)
   def __neg__(self): return Polynomial([-a for a in self])
   def __sub__(self, other): return self + (-other)
   def __abs__(self): return len(self.coefficients)
   def __call__(self, *args): return self.evaluateAt(args[0])


if __name__ == "__main__":
   f = Polynomial([1,2,3])
   g = Polynomial([4,5,6])