i'm newer in python but i have some package from other languages . Here's my question : i need to change an instance reference inside a function.This instance is passed as parameter. but i didn't know how to do it. I think i miss something in Python basics.The code bellow is given as example for what i want:
class Foo(object):
def __init__(self,a):
self.a = a
def func(a):
b = Foo(3)
a = b
var1 = Foo(5)
print(var1.a) # 5
func(var1)
print(var1.a) # it display 5 not 3
You can make func return a and then assign that to var1 as follows:
def func(a):
b = Foo(3)
a = b
return a
var1 = Foo(5)
print(var1.a) # 5
var1 = func(var1)
print(var1.a) # 3
>>> var1.a
3
What you were doing in your code is that you were changing the pointer for the local variable a in your func(a) method. However, if you want to change the var1 pointer, you have to assign the changed a variable that you passed as an argument.
One way is to use an umutable object such as the list and the property functions that automagically does what you need.
class Foo(object):
def __init__(self, value):
self._a = [value]
def __geta(self):
return self._a[0]
def __seta(self, obj):
self._a.insert(0, obj)
self._a.pop(1)
a = property(__geta, __seta)
var1 = Foo(5)
print var1.a
var1.a = 3
print(var1.a)
