Getting attribute and changing it through method

[nadav]

Hi, i have class with few getters
Lets say that one of getters return value which is also object of another class
Something like that:

class Mask(object):
def __init__(self,names): pass
def setBit(self,bit,value=False): pass
def getBit(self,bit): pass

class SNMP_ENGINE(object):
def __init__(self,params):
self._mask=Mask([])
def some_function_that_do_something_with_mask(self):pass
@property
def mask(self):
return self._mask
@mask.setter
def mask(self,value):
self._mask=value
some_function_that_do_something_with_mask()

Now, i need to write such code:

s=SNMP_ENGINE()
my_mask=s.mask
my_mask.setBit(2,True)
s.mask=my_mask

But i can't write such code:

s=SNMP_ENGINE()
s.mask.setBit(2,True) because s.mask returned object of Mask and setBit changed it but s don't know about it

Thanks for your help

[Windspar]

1. Use Code Tags. Make it so much easier to help.
2. Give a running sample.

Seem to be working.

class Mask(object):
    def __init__(self,names):
        self.bit = 8

    def setBit(self,bit,value=False):
        self.bit = bit

    def getBit(self,bit):
        return self.bit

class SNMP_Engine(object):
    def __init__(self,params):
        self._mask=Mask(None)

    def some_function_that_do_something_with_mask(self):pass

    @property
    def mask(self):
        return self._mask

    @mask.setter
    def mask(self,value):
        self._mask=value

snmp = SNMP_Engine(None)
mask = snmp.mask
mask.setBit(2, True)
#snmp.mask = mask # don't need since class is pass by reference
print(mask.bit)
print(snmp.mask.bit)

snmp.mask.setBit(4, True)
print(mask.bit)
print(snmp.mask.bit)

mask.setBit(5, True)
print(mask.bit)
print(snmp.mask.bit)

[nadav]

Thank you Windspar
Here is working example with tags

class Mask(object):
     def __init__(self,names): pass
     def setBit(self,bit,value=False): pass
     def getBit(self,bit): pass

class SNMP_ENGINE(object):
     def __init__(self,params):
        self._mask=Mask([])
     def some_function_that_do_something_with_mask(self):
         print('Do something')
     @property
     def mask(self):
        return self._mask
     @mask.setter
     def mask(self,value):
         self._mask=value
         self.some_function_that_do_something_with_mask()

print('Version 1')
s=SNMP_ENGINE(None)
my_mask=s.mask
my_mask.setBit(2,True)
s.mask=my_mask

After running we will get such print:

Version 1:
----------- Do something
Version 2:

In version 2 @mask.setter will not execute

[Windspar]

It works fine. You only have Do something print in the mask setter.

print('Version 1')
s = SNMP_ENGINE(None)
my_mask = s.mask
my_mask.setBit(2,True)
print('Version 2')
s.mask = my_mask

---

Just to let you know

s.mask = my_mask # this is the setter function

This is somewhat pointless because the object is reference.
You are just resigning the self._mask with the same data.
and calling some_function_that_do_something_with_mask.

You probably be better if Mask held a callback to some_function_that_do_something_with_mask.
sample

class Mask(object):
     def __init__(self,names, callback):
         self.names = names
         self.bit = 0
         self.value = False
         self.callback = callback

     def setBit(self,bit,value=False):
         self.bit = bit
         self.value = value
         self.callback()

     def getBit(self):
         return self.bit

class SNMP_ENGINE(object):
     def __init__(self,params):
        self._mask=Mask([], self.some_function_that_do_something_with_mask)

     def some_function_that_do_something_with_mask(self):
         print('Do something')

     @property
     def mask(self):
        return self._mask

     @mask.setter
     def mask(self,value):
         self._mask=value
         self.some_function_that_do_something_with_mask()

print('Version 1')
s = SNMP_ENGINE(None)
my_mask = s.mask
my_mask.setBit(2,True)
print('Version 2')
#s.mask = my_mask

[nadav]

Thank you Windspar
So there is not builtin mechanism in Python which update container object when child object changed?

[Windspar]

No. That what callbacks are for. How would the object know if child object updated. Without the child telling parent. Look at what I did.

So there is not builtin mechanism in Python which update container object when child object changed?

Is there a program language that you think does this.
Because I don't know of any.

---

I thought of one way. The parent would know if the child updated.
If parent was keeping a watchful eye. So the parent has a loop/function that checking for changes.
But this only happens when the parent decide to check if child objects has change.