a class variable question

[micklee74@hotmail.com]

hi
i have define a class like this

class A:
_var1 = 0
def __init__(self):
## some initialization
self.func1()

def func1():
.....
_var1 = 1
....

def getvarValue(sel f):
return _var1
I wanted var1 to be "global" inside Class A.
when i do

AnInstance = A()
AnInstance.getv arValue()

it gives me 0. It should be 1. What am i doing wrong here..thanks

[Pierre Quentel]

Re: a class variable question

In func1, _var1 = 1 creates a local variable _var1 (local to the
method), not an attribute of the instance. If you want an instance
attribute you must specify the reference to the instance by
self._var1 = 1 ; self must be passed as an attribute to func1

def func1(self):
self._var1 = 1

Similarly, in getvarValue :

def getvarValue(sel f):
return self._var1

Pierre

[Marco Wahl]

Re: a class variable question

Hi,

just some lines added below. hth

micklee74@hotma il.com wrote:[color=blue]
> hi
> i have define a class like this
>
> class A:
> _var1 = 0
> def __init__(self):
> ## some initialization
> self.func1()
>
> def func1():[/color]

self
[color=blue]
> .....
> _var1 = 1[/color]

A._var1 = 1
[color=blue]
> ....
>
> def getvarValue(sel f):
> return _var1[/color]

return A._var1
[color=blue]
> I wanted var1 to be "global" inside Class A.
> when i do
>
> AnInstance = A()
> AnInstance.getv arValue()
>
> it gives me 0. It should be 1. What am i doing wrong here..thanks[/color]

[Erik Max Francis]

Re: a class variable question

micklee74@hotma il.com wrote:
[color=blue]
> class A:
> _var1 = 0
> def __init__(self):
> ## some initialization
> self.func1()
>
> def func1():
> .....
> _var1 = 1
> ....[/color]

You mean::

class A:
_var1 = 0

...

def func1(self):
A._var1 = 1

All you're doing in your example is setting a local variable inside the
func1 method, which has no effect.

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Every path has its puddle.
-- (an English proverb)

[Erik Max Francis]

Re: a class variable question

Pierre Quentel wrote:
[color=blue]
> In func1, _var1 = 1 creates a local variable _var1 (local to the
> method), not an attribute of the instance. If you want an instance
> attribute you must specify the reference to the instance by
> self._var1 = 1 ; self must be passed as an attribute to func1
>
> def func1(self):
> self._var1 = 1[/color]

Note this only changes the attribute in the instance. If he wants it to
be changed for all other instances, he needs to change it in the class
with:: A._var1 = 1

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Every path has its puddle.
-- (an English proverb)

[Pierre Quentel]

Re: a class variable question


Erik Max Francis wrote:[color=blue]
> Note this only changes the attribute in the instance. If he wants it to
> be changed for all other instances, he needs to change it in the class
> with:: A._var1 = 1[/color]

Yes, but in the OP's code func1() is called by __init__ for every
instance - which in fact makes declaring _var1 as a class attribute
useless

Anyway, I find that changing the class attribute by calling a method on
an instance is a little confusing. I would rather set the class
attribute like this :

class A2:

_var1 = 0

def getvarValue(sel f):
return self._var1

a = A2()
print a.getvarValue()[color=blue][color=green][color=darkred]
>>> 0[/color][/color][/color]
A2._var1 = 0 # change class attribute
print a.getvarValue()[color=blue][color=green][color=darkred]
>>> 1[/color][/color][/color]
b = A2()
print b.getvarValue()[color=blue][color=green][color=darkred]
>>> 1[/color][/color][/color]

Or using a class method :

class A3:

_var1 = 0

@classmethod
def func1(cls):
cls._var1 = 1

def getvarValue(sel f):
return self._var1

a = A3()
print a.getvarValue()[color=blue][color=green][color=darkred]
>>> 0[/color][/color][/color]
A3.func1() # change class attribute
print a.getvarValue()[color=blue][color=green][color=darkred]
>>> 1[/color][/color][/color]
b = A3()
print b.getvarValue()[color=blue][color=green][color=darkred]
>>> 1[/color][/color][/color]

Pierre

[Steve Holden]

Re: a class variable question

Erik Max Francis wrote:
[...][color=blue]
> All you're doing in your example is setting a local variable inside the
> func1 method, which has no effect.
>[/color]
I think EMF was thinking, but failed to write, "outside the function" at
the end of that sentence ;-)

regards
Steve
--
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC/Ltd http://www.holdenweb.com
Love me, love my blog http://holdenweb.blogspot.com
Recent Ramblings http://del.icio.us/steve.holden

[Bruno Desthuilliers]

Re: a class variable question

micklee74@hotma il.com wrote:[color=blue]
> hi
> i have define a class like this
>[/color]
# class A:
class A(object):[color=blue]
> _var1 = 0
> def __init__(self):
> ## some initialization
> self.func1()
>[/color]
# def func1():
def func1(self):[color=blue]
> .....[/color]
# _var1 = 1
self.__class__. _var1 = 1
# or if func1() does'nt use any instance attributes:
# @classmethod
# def func1(cls):
# ....
# cls._var1 = 1
[color=blue]
> def getvarValue(sel f):[/color]
# return _var1
return self.__class__. _var1
[color=blue]
> I wanted var1 to be "global" inside Class A.[/color]

The name is "class attribute".



--
bruno desthuilliers
python -c "print '@'.join(['.'.join([w[::-1] for w in p.split('.')]) for
p in 'onurb@xiludom. gro'.split('@')])"