class inheritance python2.7 vs python3.3

[jwe.van.dijk at gmail.com]

On Monday, 6 January 2014 18:14:08 UTC+1, jwe.va... at gmail.com  wrote:
> I have problems with these two classes:
> 
> 
> 
> class LPU1():
> 
>     def __init__(self, formula):
> 
>         """
> 
>         formula is a string that is parsed into a SymPy function
> 
>         and several derived functions
> 
>         """
> 
>         self.formula = formula
> 
>         ... ...
> 
> 
> 
> class LPU3(LPU1):
> 
>         def __new__(self):
> 
>         """
> 
>         the same functions as LPU1 but some added functions
> 
>         and some functions redefined
> 
>         """
> 
>         ... ...
> 
> 
> 
> if __name__ == '__main__:
> 
>     y = y = 'x_0 * x_1 + x_2'
> 
>     stats1 = LPU1(y)
> 
>     stats3 = LPU3(y)
> 
> 
> 
> Worked perfectly on Python 2.7.5+ but on Python 3.3.2+ I get on instantiatiating stat3:
> 
> TypeError: __new__() takes 1 positional argument but 2 were given
> 
> 
> 
> What am I doing wrong?
> 
> I must confess I am a bit out of my depth here so any explanation will be a learning experience.
> 
> 
> 
> Many thanks, Janwillem

Thanks for all the contributions. I now have:
class LPU1(object):
    def __init__(self, formula):
    ... ...
and
class LPU3(LPU1):
    def __init__(self, y):
        LPU1.__init__(self, y)
       ... ...

which gives the correct results both on 2.7 and 3.3.
Is that more or less good practice?
Now I stumble on a SymPy problem under 3.3 but that obviously is an other topic
Cheers, janwillem