Implements a plus-or-minus "operator", +OR-

plusorminus.py

import itertools
import math

class _OR(object):
    def __radd__(self, lhs):
        if isinstance(lhs, PlusOrMinus):
            copy = PlusOrMinus(*lhs)
        else:
            copy = PlusOrMinus(lhs)
        copy.plusorminus = True
        return copy

OR = _OR()

class PlusOrMinus(tuple):
    def __new__(cls, *elements):
        return super(PlusOrMinus, cls).__new__(cls, elements)
    def __init__(self, *elements):
        super(PlusOrMinus, self).__init__(*elements)
        self.plusorminus = False
    def __add__(self, rhs):
        if rhs is OR:
            return NotImplemented
        return PlusOrMinus(*(v+rhs for v in self))
    def __sub__(self, rhs):
        if self.plusorminus:
            return PlusOrMinus(*itertools.chain(*((v+rhs, v-rhs) for v in self)))
        else:
            return PlusOrMinus(*(v-rhs for v in self))
    def __mul__(self, rhs):
        return PlusOrMinus(*(v*rhs for v in self))
    def __div__(self, rhs):
        return PlusOrMinus(*(v/rhs for v in self))
    def __mod__(self, rhs):
        return PlusOrMinus(*(v%rhs for v in self))
    def __pow__(self, rhs):
        return PlusOrMinus(*(v**rhs for v in self))

def quadratic_formula(a, b, c): 
    return (-b +OR- math.sqrt(b**2 - 4*a*c)) / (2*a)

if __name__ == '__main__':
    a = 1 +OR- 5
    print 'a = 1 +OR- 5   =', a
    b = a +OR- 0.5
    print 'b = a +OR- 0.5 =', b
    c = b + 10
    print 'c = b + 10     =', c
    x = quadratic_formula(1, 3, -4)
    print 'quadratic_formula(1, 3, -4) =', x

# a = 1 +OR- 5   = (6, -4)
# b = a +OR- 0.5 = (6.5, 5.5, -3.5, -4.5)
# c = b + 10     = (16.5, 15.5, 6.5, 5.5)
#
# quadratic_formula(1, 3, -4) = (1.0, -4.0)