subclassing list and adding other variables ?

[GrelEns]

hello,

i wonder if this possible to subclass a list or a tuple and add more
attributes ? also does someone have a link to how well define is own
iterable object ?

what i was expecting was something like :
[color=blue][color=green][color=darkred]
>>> t = Test('anAttribu teValue', ['el1', 'el2'])
>>> t.anAttribute[/color][/color][/color]
'anAttributeVal ue'[color=blue][color=green][color=darkred]
>>> for x in t:[/color][/color][/color]
print x
el1
el2

and below are some real unsuccessful tests :
[color=blue][color=green][color=darkred]
>>> class Test(tuple):[/color][/color][/color]
def __init__(self, a, alist):
self.a = a
self = tuple(alist)

[color=blue][color=green][color=darkred]
>>> t = Test(1, (1,2,3))[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#486>" , line 1, in -toplevel-
t = Test(1, (1,2,3))
TypeError: tuple() takes at most 1 argument (2 given)[color=blue][color=green][color=darkred]
>>> class Test(tuple):[/color][/color][/color]
def __init__(self, (a, alist)):
self.a = a
self = tuple(alist)

[color=blue][color=green][color=darkred]
>>> t = Test((1, (1,2,3)))
>>> t.a[/color][/color][/color]
1[color=blue][color=green][color=darkred]
>>> t.a = 2
>>> t.a[/color][/color][/color]
2[color=blue][color=green][color=darkred]
>>> len(t)[/color][/color][/color]
2[color=blue][color=green][color=darkred]
>>> t[/color][/color][/color]
(1, (1, 2, 3))[color=blue][color=green][color=darkred]
>>> t[2][/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#495>" , line 1, in -toplevel-
t[2]
IndexError: tuple index out of range[color=blue][color=green][color=darkred]
>>> t[1][/color][/color][/color]
(1, 2, 3)[color=blue][color=green][color=darkred]
>>> class Test(tuple):[/color][/color][/color]
def __init__(self, (a, alist)):
self.__init__(t uple(alist))
self.a = a

[color=blue][color=green][color=darkred]
>>> t = Test((1, (1,2,3)))[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#500>" , line 1, in -toplevel-
t = Test((1, (1,2,3)))
File "<pyshell#499>" , line 3, in __init__
self.__init__(t uple(alist))
File "<pyshell#499>" , line 2, in __init__
def __init__(self, (a, alist)):
ValueError: unpack tuple of wrong size[color=blue][color=green][color=darkred]
>>> class Test(tuple):[/color][/color][/color]
def __init__(self, alist, a = None):
self.__init__(t uple(alist))
self.a = a

[color=blue][color=green][color=darkred]
>>> t = Test((1,2,3), 4)[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#503>" , line 1, in -toplevel-
t = Test((1,2,3), 4)
TypeError: tuple() takes at most 1 argument (2 given)[color=blue][color=green][color=darkred]
>>> class Test(tuple):[/color][/color][/color]
def __init__(self, (alist, a = None)):
self.__init__(t uple(alist))
self.a = a

SyntaxError: invalid syntax[color=blue][color=green][color=darkred]
>>>
>>> class Test(list):[/color][/color][/color]
def __init__(self, (a, alist)):
self.a = a
self = tuple(alist)

[color=blue][color=green][color=darkred]
>>> t = Test((4, (1,2,3)))
>>> t[/color][/color][/color]
[][color=blue][color=green][color=darkred]
>>> class Test(list):[/color][/color][/color]
def __init__(self, (a, alist)):
self.a = a
self = alist

[color=blue][color=green][color=darkred]
>>> t = Test((4, (1,2,3)))
>>> t[/color][/color][/color]
[][color=blue][color=green][color=darkred]
>>> t.a[/color][/color][/color]
4[color=blue][color=green][color=darkred]
>>> len(t)[/color][/color][/color]
0[color=blue][color=green][color=darkred]
>>> class Test(list):[/color][/color][/color]
def __init__(self, a, alist):
self.a = a
self = alist

[color=blue][color=green][color=darkred]
>>> t = Test(4, (1,2,3))
>>> t[/color][/color][/color]
[][color=blue][color=green][color=darkred]
>>> t.a[/color][/color][/color]
4[color=blue][color=green][color=darkred]
>>> class Test(list):[/color][/color][/color]
def __init__(self, a, alist):
self.a = a
self.__init__(a list)

[color=blue][color=green][color=darkred]
>>> t = Test(4, (1,2,3))[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#523>" , line 1, in -toplevel-
t = Test(4, (1,2,3))
File "<pyshell#522>" , line 4, in __init__
self.__init__(a list)
TypeError: __init__() takes exactly 3 arguments (2 given)

[GrelEns]

Re: subclassing list and adding other variables ?


"GrelEns" <grelens@NOSPAM yahoo.NOTNEEDED fr> a écrit dans le message de news:
4050d0df$0$289$ 626a14ce@news.f ree.fr...[color=blue]
> hello,
>
> i wonder if this possible to subclass a list or a tuple and add more
> attributes ? also does someone have a link to how well define is own
> iterable object ?
>
> what i was expecting was something like :
>[color=green][color=darkred]
> >>> t = Test('anAttribu teValue', ['el1', 'el2'])
> >>> t.anAttribute[/color][/color]
> 'anAttributeVal ue'[color=green][color=darkred]
> >>> for x in t:[/color][/color]
> print x
> el1
> el2[/color]

i reply to myself, but still have questions ;)

so this one works :
[color=blue][color=green][color=darkred]
>>> class Test(list):[/color][/color][/color]
def __init__(self, a):
self.a = a
def load(self, alist):
self.extend(ali st)

[color=blue][color=green][color=darkred]
>>> t = Test(4)
>>> t[/color][/color][/color]
[][color=blue][color=green][color=darkred]
>>> t.load((1,2,3))
>>> t[/color][/color][/color]
[1, 2, 3]

what do you think of such a design ? is there some underlying flaw that i
should be aware of ?

(and about the tuple stuffs not working in my previous examples, i suppose
this is because a tuple is immutable and thus should not be modified after
creation)

thx

[Gerrit]

Re: subclassing list and adding other variables ?

GrelEns wrote:[color=blue]
> i wonder if this possible to subclass a list or a tuple and add more
> attributes ? also does someone have a link to how well define is own
> iterable object ?[/color]

For subclassing builtin types, read:

http://www.python.org/2.2.3/descrintro.html#subclassing

Gerrit.

--
Weather in Twenthe, Netherlands 11/03 20:25 UTC:
2.0°C wind 2.7 m/s E (57 m above NAP)
--
Asperger's Syndrome - a personal approach:

http://people.nl.linux.org/~gerrit/english/

[Peter Otten]

Re: subclassing list and adding other variables ?

GrelEns wrote:
[color=blue]
> i wonder if this possible to subclass a list or a tuple and add more
> attributes ? also does someone have a link to how well define is own
> iterable object ?[/color]

[You tried hard]

With lists it is the standard procedure of overriding __init__() and calling
the baseclass method:
[color=blue][color=green][color=darkred]
>>> class List(list):[/color][/color][/color]
.... def __init__(self, iterable, a):
.... list.__init__(s elf, iterable)
.... self.a = a
....[color=blue][color=green][color=darkred]
>>> a = List((1,2,3), "abc")
>>> a[/color][/color][/color]
[1, 2, 3][color=blue][color=green][color=darkred]
>>> a.a[/color][/color][/color]
'abc'

Tuples are immutable and thus changes in __init__() will not affect the
tuple items. They are set in the __new__() method instead.
[color=blue][color=green][color=darkred]
>>> class Tuple(tuple):[/color][/color][/color]
.... def __new__(cls, *args):
.... return tuple.__new__(c ls, args[0])
.... def __init__(self, seq, a):
.... self.a = a
....[color=blue][color=green][color=darkred]
>>> b = Tuple((1,2,3), "abc")
>>> b[/color][/color][/color]
(1, 2, 3)[color=blue][color=green][color=darkred]
>>> b.a[/color][/color][/color]
'abc'

For a minimal iterable class, let __iter__() return self and next()
calculate the next value or raise a StopIteration exception when there are
no more values:
[color=blue][color=green][color=darkred]
>>> class Iterable:[/color][/color][/color]
.... def __init__(self, start, maxval):
.... self.value = start
.... self.maxval = maxval
.... def __iter__(self): return self
.... def next(self):
.... if self.value > self.maxval:
.... raise StopIteration
.... result = self.value
.... self.value *= -2
.... return result
....[color=blue][color=green][color=darkred]
>>> for n in Iterable(1, 500):[/color][/color][/color]
.... print n,
....
1 -2 4 -8 16 -32 64 -128 256 -512

(I've got a hunch that Iterator would have been a more appropriate name, but
you may judge on your own, see
http://www.python.org/doc/current/tut/node17.html)

Peter

[GrelEns]

Re: subclassing list and adding other variables ?


"Peter Otten" <__peter__@web. de> a écrit dans le message de news:
c2qr32$j1n$01$1 @news.t-online.com...[color=blue]
> GrelEns wrote:
>[color=green]
> > i wonder if this possible to subclass a list or a tuple and add more
> > attributes ? also does someone have a link to how well define is own
> > iterable object ?[/color]
>
> With lists it is the standard procedure of overriding __init__() and[/color]
calling[color=blue]
> the baseclass method:
>[color=green][color=darkred]
> >>> class List(list):[/color][/color]
> ... def __init__(self, iterable, a):
> ... list.__init__(s elf, iterable)
> ... self.a = a
> ...[color=green][color=darkred]
> >>> a = List((1,2,3), "abc")
> >>> a[/color][/color]
> [1, 2, 3][color=green][color=darkred]
> >>> a.a[/color][/color]
> 'abc'[/color]

thanks, so i supposed that this is a correct way to do :
[color=blue][color=green][color=darkred]
>>> class List(list):[/color][/color][/color]
def __init__(self, v = None):
self.v = v
def load(self, values):
list.extend(sel f, values)
def gets(self):
return list(self)
[color=blue][color=green][color=darkred]
>>> l = List(5)
>>> l.load([1,2,3])
>>> l[/color][/color][/color]
[1, 2, 3][color=blue][color=green][color=darkred]
>>> l.gets()[/color][/color][/color]
[1, 2, 3][color=blue][color=green][color=darkred]
>>> type(l.gets())[/color][/color][/color]
<type 'list'>[color=blue][color=green][color=darkred]
>>> type(l)[/color][/color][/color]
<class '__main__.List' >

BTW while i think i get it with the list.extend(sel f, values) which is i
suppose

super_class.met hod_from_super_ class(my_curren t_instance, *ohers_args)

i feel quite unhappy with the return list(self) which for me is rather a
call to the builtin function list() upon the current instance , how could i
write this particular :

super_class.att ribute_containi ng_content_of(m y_current_insta nce)

also, which are the method to overwrite for a class subclassing a list to
automatically call the load() method if the list is empty ?

thx for your help.