overloading constructor in python?

[lennart@kommunicera.umea.se]

This is probably a really stupid question, but I cant seem to find a
satisfying answer by myself so here it goes. In for example java we
could create a class dummie with several constructors, say one that
takes an int, and one that takes a String as argument. In python it
doesnt seem possible to have several __init__ methods ( and I assume if
we could there would be some problem to determine which __init__ to
use). So my question is how this is normally solved in python? I dont
really like the idea of using neither

def __init__(self, o):
if type(o) is ...

nor subclasses for the baseclass, but I cant think of another way. Any
thoughts anyone?

Thanx
/Lennart

[Larry Bates]

Re: overloading constructor in python?

lennart@kommuni cera.umea.se wrote:[color=blue]
> This is probably a really stupid question, but I cant seem to find a
> satisfying answer by myself so here it goes. In for example java we
> could create a class dummie with several constructors, say one that
> takes an int, and one that takes a String as argument. In python it
> doesnt seem possible to have several __init__ methods ( and I assume if
> we could there would be some problem to determine which __init__ to
> use). So my question is how this is normally solved in python? I dont
> really like the idea of using neither
>
> def __init__(self, o):
> if type(o) is ...
>
> nor subclasses for the baseclass, but I cant think of another way. Any
> thoughts anyone?
>
> Thanx
> /Lennart
>[/color]
In python it is called duck typing but you don't need separate
constructors:

def __init__(self, c):
if isinstance(c, int): ...do stuff...
elif isinstance(c, list): ...do stuff...
elif isinstance(c, tuple): ...do stuff...
else:

[lennart@kommunicera.umea.se]

Re: overloading constructor in python?


Larry Bates wrote:
[...][color=blue]
> In python it is called duck typing but you don't need separate
> constructors:
>
> def __init__(self, c):
> if isinstance(c, int): ...do stuff...
> elif isinstance(c, list): ...do stuff...
> elif isinstance(c, tuple): ...do stuff...
> else:
> .
> .
> .
>
> Remember Python doesn't care what c is and doesn't do
> type checking so you can do anything you want.
>[/color]

Thanx for the info.

/Lennart



[color=blue]
> -Larry Bates[/color]

[Jarek Zgoda]

Re: overloading constructor in python?

Larry Bates napisa³(a):
[color=blue]
> In python it is called duck typing but you don't need separate
> constructors:
>
> def __init__(self, c):
> if isinstance(c, int): ...do stuff...
> elif isinstance(c, list): ...do stuff...
> elif isinstance(c, tuple): ...do stuff...
> else:
> .
> .
> .
>
> Remember Python doesn't care what c is and doesn't do
> type checking so you can do anything you want.[/color]

This is no better than type checking. And this doesn't remind "duck
typing" at all.

--
Jarek Zgoda

http://jpa.berlios.de/

[Paddy]

Re: overloading constructor in python?

I guess in python we use two idioms to cover most of the uses of
mulltiple constructors:
1) Duck typing were for example if you do:

class C1(object):
def __init__(self, n):
n = float(n)

n could be an integer, a floating point number,, or a string
representing a float.

2) Default values to parameters:

class C2(object):
def __init__(self, x=None, y=None, s=""):
pass

C2 can be initialised with any one, two, three, or zero arguments;
those not given would take the default values shown to the right of the
equals sign above.

- Cheers, Paddy.
--
Signs of spring here in the west-country.

[Alex Martelli]

Re: overloading constructor in python?

Paddy <paddy3118@nets cape.net> wrote:
[color=blue]
> I guess in python we use two idioms to cover most of the uses of
> mulltiple constructors:
> 1) Duck typing were for example if you do:
>
> class C1(object):
> def __init__(self, n):
> n = float(n)
>
> n could be an integer, a floating point number,, or a string
> representing a float.
>
> 2) Default values to parameters:
>
> class C2(object):
> def __init__(self, x=None, y=None, s=""):
> pass[/color]

.... and classmethods. OK, _three_ idioms. Oh, and factory functions.
Among the idioms we use are the following...


Alex

[Jon Ribbens]

Re: overloading constructor in python?

In article <1hd8g42.t78sge 1tuys90N%aleaxi t@yahoo.com>, Alex Martelli wrote:[color=blue][color=green]
>> I guess in python we use two idioms to cover most of the uses of
>> mulltiple constructors:[/color]
>
> ... and classmethods. OK, _three_ idioms. Oh, and factory functions.
> Among the idioms we use are the following...[/color]

Nobody expects the Spanglish inquisition...