Sorry for the vague title. Probably best to just show you the code that explains it better.
This is a simplified example of what I want to do:
# THIS DOESN'T WORK
from random import choice
class Expr(object):
"""
Expr(expr, op, val) -> an expression object.
"""
def __init__(self, expr, op='', val=''):
self.expr = expr # can be another instance of Expression.
self.op = op
self.val = val
def __str__(self):
return ("%s %s %s" % (self.expr, self.op, self.val)).strip()
def expand(self):
self = Expr(self, choice('+-*/'), choice('12345'))
Then I tried messing around with Expr.__new__() and Expr.__init__() but that didn't work.
The only way I've got it to work is by doing the expanding part outside of the object, by a method of some other class. But I want the Expr class to be responsible for itself. How can I do this and why doesn't the above work?
