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From: Peter Otten on 8 Jun 2010 13:36
Jason Scheirer wrote:

> On Jun 8, 9:37 am, Peter Otten <__pete...(a)web.de> wrote:
>> Ross Williamson wrote:
>> > Hi Everyone,
>>
>> > Just a quick question - Is it possible to assign class variables in
>> > the __init__() - i.e. somthing like:
>>
>> > def __init__(self,self.source = "test", self.length = 1)
>>
>> > rather than
>>
>> > def __init__(self,source = "test", length = 1):
>>
>> No. If you are just lazy, try
>>
>> >>> import sys
>> >>> def update_self():
>>
>> ... d = sys._getframe(1)
>> ... d = d.f_locals
>> ... self = d.pop("self")
>> ... for k, v in d.iteritems():
>> ... setattr(self, k, v)
>> ...>>> class A(object):
>>
>> ... def __init__(self, source="test", length=1):
>> ... update_self()
>> ... def __repr__(self):
>> ... return "A(source=%r, length=%r)" % (self.source,
>> self.length)
>> ...>>> A()
>>
>> A(source='test', length=1)>>> A(length=42)
>>
>> A(source='test', length=42)
>>
>> Personally, I prefer explicit assignments inside __init__().
>>
>> Peter
>
> Or more simply
>
> def __init__(self, source = "test", length = 1):
> for (k, v) in locals().iteritems():
> if k != 'self':
> setattr(self, k, v)

The idea was that you put update_self() into a module ready for reuse...

Peter
From: Jean-Michel Pichavant on 8 Jun 2010 13:58
Peter Otten wrote:
> Jason Scheirer wrote:
>
>
>> On Jun 8, 9:37 am, Peter Otten <__pete...(a)web.de> wrote:
>>
>>> Ross Williamson wrote:
>>>
>>>> Hi Everyone,
>>>>
>>>> Just a quick question - Is it possible to assign class variables in
>>>> the __init__() - i.e. somthing like:
>>>>
>>>> def __init__(self,self.source = "test", self.length = 1)
>>>>
>>>> rather than
>>>>
>>>> def __init__(self,source = "test", length = 1):
>>>>
>>> No. If you are just lazy, try
>>>
>>>
>>>>>> import sys
>>>>>> def update_self():
>>>>>>
>>> ... d = sys._getframe(1)
>>> ... d = d.f_locals
>>> ... self = d.pop("self")
>>> ... for k, v in d.iteritems():
>>> ... setattr(self, k, v)
>>> ...>>> class A(object):
>>>
>>> ... def __init__(self, source="test", length=1):
>>> ... update_self()
>>> ... def __repr__(self):
>>> ... return "A(source=%r, length=%r)" % (self.source,
>>> self.length)
>>> ...>>> A()
>>>
>>> A(source='test', length=1)>>> A(length=42)
>>>
>>> A(source='test', length=42)
>>>
>>> Personally, I prefer explicit assignments inside __init__().
>>>
>>> Peter
>>>
>> Or more simply
>>
>> def __init__(self, source = "test", length = 1):
>> for (k, v) in locals().iteritems():
>> if k != 'self':
>> setattr(self, k, v)
>>
>
> The idea was that you put update_self() into a module ready for reuse...
>
> Peter
>
still

def __init__(self, source="test", length=1):
self.source = source
self.length = length

is the way to go. OP's original idea is a bad idea :).
Could be a problem with hundreds of parameters, but who write
constructors with hundreds of parameters ?

JM
From: Peter Otten on 8 Jun 2010 14:09
Jean-Michel Pichavant wrote:

> def __init__(self, source="test", length=1):
> self.source = source
> self.length = length
>
> is the way to go. OP's original idea is a bad idea :).

D'accord.

> Could be a problem with hundreds of parameters, but who write
> constructors with hundreds of parameters ?


From: danieldelay on 8 Jun 2010 14:17
you can also use :

>>> class A(object):
def __init__(self, **args):
self.__dict__.update(args)

>>> a=A(source='test', length=2)
>>> a.source
'test'

but this is to be used carefully because mispelling your args somewhere
in your program will not raise any error :
>>> A(sourc='test', lenth=2)

Daniel
From: Mark Lawrence on 8 Jun 2010 16:36
On 08/06/2010 17:55, Steven D'Aprano wrote:
> On Tue, 08 Jun 2010 17:24:55 +0100, Mark Lawrence wrote:
>
>> On 08/06/2010 17:04, Ross Williamson wrote:
>>> Hi Everyone,
>>>
>>> Just a quick question - Is it possible to assign class variables in the
>>> __init__() - i.e. somthing like:
>>
>> They're instance variables, not class variables.
>
> In the usual Python terminology, they're instance *attributes*. If a
> float variable is a variable storing a float, and a string variable is a
> variable storing a string, then in a language like Python where classes
> are first-class objects a class variable is a variable storing a class.
>
> That's why Python has functions getattr, setattr and delattr, and special
> methods __getattr__ etc., rather than "getvar" etc.
>
> I realise that other languages use "class variable" and "instance
> variable" to mean something completely different, but we don't have to
> emulate their mistakes... *wink*
>
Yes alright bloody Aussies ** n * sodit * *wink*. Not sure if this is
a syntax error, but too lazy too test at an interactive prompt.

Kindest regards.

Mark Lawrence.

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