__init__ function arguments

[CoderMan]

Hello,

I am trying to make an __init__ function's argument be the previous argument of that function divided by 2.

class item:
    def __init__(self,value1,value2):
        self.v1 = value1
        self.v2 = value2

x = item(10,item.v1/2)

However, when I run it I get the message that "type object 'item' has no attribute v1".

Any other ways to do it?

[Larz60+]

the statement:

x = item(10,item.v1/2)

is outside of the class, so cannot see v1 or v2

this script is not worthy of a class, but:
better to use inside of a function like:

class item:
    def __init__(self,value1,value2):
        self.v1 = value1
        self.v2 = value2

def testit():
    myitem = item(45, 78)
    ...
    # some time later
    x = item(10, myitem.v1/2)

if __name__ == '__main__':
    testit()

[snippsat]

Maybe a little confusing to instantiate both myitem and x Larz60+,as it not clear that both is needed.

Here the basic.

class Item:
    def __init__(self, value1, value2):
        self.v1 = value1
        self.v2 = value2

Use class:

>>> # Instantiate the Item object
>>> x = Item(8, 4)

>>> # Access the instance attributes
>>> x.v1
8
>>> x.v2
4

>>> # At this point you can what you want instance attributes
>>> x.v1 + x.v2 / 2
10.0
>>> x.v1 + x.v2 * 20 / x.v1
18.0

[CoderMan]

the statement:

x = item(10,item.v1/2)

is outside of the class, so cannot see v1 or v2

this script is not worthy of a class, but:
better to use inside of a function like:

class item:
    def __init__(self,value1,value2):
        self.v1 = value1
        self.v2 = value2

def testit():
    myitem = item(45, 78)
    ...
    # some time later
    x = item(10, myitem.v1/2)

if __name__ == '__main__':
    testit()

Larz60+ thank you so much, but I just realized I made a mistake in the example!! I meant

x = item(10, x.v1/2)

So sorry for this, I really appreciate the reply from both you and snippsat!

[stullis]

You cannot reference x.v1 as an argument to the __init__() method because x doesn't exist yet. The class and its attributes aren't instantiated until after the __init__() method has completed. Until then, the attributes cannot be accessed.