Hi,
Le Friday 13 June 2008 15:24:31 Dummy Pythonese Luser, vous avez écrit :
> Greetings *.*:
>
> The following program caused an error and puzzled me to no end. Any help
> immensely appreciated.
>
>
> class Second(First):
> def __init__(self, datestr):
> y = int(datestr[0:4])
> m = int(datestr[4:6])
> d = int(datestr[6:8])
> First.__init__(self, y, m, d)
>
> # a = Second("20060201")
> # TypeError: function takes exactly 3 arguments (1 given)
> # Why?
probably because date is an immutable type, so the init stuff is done in
__new__ and not __init__ (and thus __new__ expects the same args as
__init__). So you should replace First and Second __init__ methods by
something like this :
def __new__ (cls, datestr):
y = int(datestr[0:4])
m = int(datestr[4:6])
d = int(datestr[6:8])
self = date.__new__(cls, y, m, d)
return self
The general rule is to do your initialization in __new__ for immutable types
and in __init__ for mutable ones. See the chapter 3 of the reference manual
(data model) for more infos.
--
Cédric Lucantis
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