Returning 'None' on Instantiation ?

[Emile van Sebille]

The Object self is created before __init__ populates it and survives
__init__.  You could use __nonzero__ to meet your example's needs:

>>> class myClass:
 def __init__(self, arg):
  self.isValid = 1
  if arg < 5:
   self.isValid = 0
 def __nonzero__(self):
  return self.isValid


>>> a = myClass(3)
>>> if a: print "OK"

>>> b = myClass(8)
>>> if b: print "OK"

OK
>>>


HTH,

Emile van Sebille
emile at fenx.com

---------
----- Original Message -----
From: "Dave Haynes" <Dave.Haynes at sia-mce.co.uk>
Newsgroups: comp.lang.python
Sent: Friday, June 01, 2001 6:28 AM
Subject: Returning 'None' on Instantiation ?


> Is there a way to optionally return 'None' on instantiation? I'm
> thinking of something like the following:
>
> class myClass:
>     def __init__(self, param):
>
>         if <check param>:
>             <initialise data members>
>         else:
>             <make self a 'None object'>
>
>
> myParam = GetParam()
> myObj = myClass(myParam)
>
> if myObj:
>     print 'Okay'
> else:
>     print 'Couldn't make myObj from myParam'
>
>  This is a fairly common state of affairs. If there's nothing specific
> in Python to accomodate this, what methods are considered robust by
> this NG?
>
>
>                        Best Regards,
>
>
>                                              Dave.