Re: TypeError with date class

[=?utf-8?q?C=C3=A9dric_Lucantis?=]

Hi,

Le Friday 13 June 2008 15:24:31 Dummy Pythonese Luser, vous avez écritÂ*:

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