Still the __new__ hell ...

[Paul McGuire]

On Mar 17, 4:31 pm, Paulo da Silva <psdasil... at esotericaX.ptX> wrote:
> Sorry to put here too many questions about __init__ __new__
> stuff but I always found a new problem when using them.
> I have searched for simple __new__ docs on how to do the
> basic things but find none.
>
> After trying the solutions people gently posted here
> (thanks) I run into new trouble when I go with further
> development.
>
> Here is the new situation.
>
> As suggested in a previous post, I used __new__ to
> subclass date class but now cPickle/pickle loads
> does not work.
>
> from datetime import date
> import cPickle,string
>
> class MyDate(date):
>         def __new__(cls,year,month=None,day=None):
>                 if type(year) is str:
>                         year,month,day=map(int,string.split(year,'-'))
>                 if year<100:
>                         year+=2000
>                 return date.__new__(cls,year,month,day)
>
> class C1(object):
>         def __init__(self):
>                 self.x=MyDate("2007-3-15")
>
>         def f(self):
>                 print self.x
>
> c1=C1()
>
> d=cPickle.dumps(c1)
> c2=cPickle.loads(d)
> c2.f()
>
> 1. year is passed to __new__ as a string but with invalid
> contents!
>
> 2. If I had a __new__ in class C1, cPickle.loads invokes it
> with only one parameter. This forces to allow __new__ accept
> only 1 parameter (cls) which I don't want for the normal
> situation.
>
> Thanks for your patience.
> Paulo

Any special reason you have to use __new__ for this factory method?
This version works, without the problems with __new__:

def getDate(*args):
    if isinstance(args[0],basestring):
        year,month,day = map(int,string.split(args[0],'-'))
    else:
        year,month,day = args
    if year < 100:
        year += 2000
    return date(year,month,day)

class C1(object):
        def __init__(self):
                #self.x=MyDate("2007-3-15")
                self.x = getDate("2007-3-15")

        def f(self):
                print self.x


-- Paul