Converting between objects
bignose+hates-spam at benfinney.id.au
Fri Jul 20 01:00:57 CEST 2007
"Nathan Harmston" <ratchetgrid at googlemail.com> writes:
> I have being thinking about this and was wondering with built in types
> you can do things like
Calls the constructor for the 'float' type, passing the integer 1; the
constructor returns a new float object.
Calls the constructor for the 'str' type, passing the integer 200; the
constructor returns a new str object.
> is there way I can define conversion functions like this
These are not "conversion functions"; they are the constructors of the
You can hook into the instance creation by modifying the '__new__'
method of the metaclass; but probably the easier way is to hook into
the instance initialisation (after it is created) by modifying the
'__init__' method of the class.
> say i have a class A and a class B
> bobj = B()
> aobj = a(bobj)
> in a neater way than just defining a set of methods
> def a(object_to_convert)
> # if object_to_convert of type......
> # do some stuff
> return A()
Rather than this, define '__init__' to do some stuff to 'self', that
is, modify attributes of the instance during its initialisation. The
'__init__' method is automatically called during object initialisation
and receives all the parameters that were passed to the constructor.
def __init__(self, obj):
self.foo = do_stuff(obj)
aobj = B(42)
\ "Pinky, are you pondering what I'm pondering?" "Wuh, I think |
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