Implementing formula notation in python

formula.py

# Here's a small experiment in hacking together a formula notation for 
# Python, in the style of R. This is without reference to any matrices, but 
# it's pretty straightforward to see how one might plug such a system into a 
# matrix library.

# I bet this could easily extend to other R formula features.

class Predictor(object):
    def __init__(self,label):
        self.label = label
    
    def __add__(self, next):
        return PredictorSet(self, next)
    
    def __str__(self):
        return self.label

class PredictorSet(object):
    def __init__(self, *args):
        self.preds = args
    
    def __add__(self, next):
        self.preds.append(next)
    
    def __str__(self):
        return ' + '.join([str(p) for p in self.preds])

class Response(object):
    
    def __init__(self, label):
        self.label = label
    
    def __or__(self, predictor_set):
        return Formula(self, predictor_set)

    def __str__(self):
        return self.label

class Formula(object):
    def __init__(self, r, p):
        self.r = r
        self.p = p
    
    def __str__(self):
        return str(self.r) + ' | ' + str(self.p)  

if __name__ == "__main__":
    # Ignore the fact that you have to define variables like this.
    # The point is the formula class instantiation AS a formula,
    # and not the var defs. That can easily be solved alongside a 
    # worthwhile data frame implementation.
    a = Response('return')
    b = Predictor('age')
    c = Predictor('weight')


   # this gives you an object of type 'Formula'.  Bam.    
    formula = a | b + c
    
    print formula