How to access and change(class) init method attributes from another function in python?

Question

Recently I was trying to access an __init__ method attribute to change its values and recalculate some properties automatically from another function.

I have tried some basic approaches and did not succeed to obtain what I wanted. This is the code in question:

class Square():
     def __init__(self, length, width):
         self.length = length
         self.width = width

     @property
     def Area(self):
         return self.length * self.width

A1 = Square(length=3, width=3) ## made an object
print(A1.Area) #9

def check():
    a = []
    b = [1,3,2]
    t = [100,20,23]
    d = [0.1]
    c = 4
    for i in d:
        c += 6
        d += [0.1]
        if A1.Area < 8: ## eg. if A1.length=2 and A1.width=2 have been changed in the  __init__ attribute this A1.Area would be 4 and the condtion is ture and the loop break ends
            break ## here break the loop finally  if the A1.Area is altered by the conditions 
        for k in range(len(b)):
            a.append(c + b[k])
            if c + b[k] > t[2]:
                A1.length = 2## here i am trying to change the __init__ attribute
                A1.width = 2 ## here i am trying to change the __init__ attribute
                print(k)
                c = c - 6
                break
    return c

what do you mean? A1=Square(length=3,width=3) i defined the Square instances not the Square attribute? — jack
– jack, Commented Aug 13, 2014 at 11:01
What is the exact problem ? You can't change length and width ? — Dimitri Mockelyn
– Dimitri Mockelyn, Commented Aug 13, 2014 at 11:02
Well, you had it right. That's the way you change an attribute. You should check whether you enter this if loop or not. If A1 never changes, my guess would be that you never have c+b[k]>t[2] — Dimitri Mockelyn
– Dimitri Mockelyn, Commented Aug 13, 2014 at 11:09
If it's a Square - why does it need a length and a width ? — Jon Clements
– Jon Clements, Commented Aug 13, 2014 at 11:16
@Jack if it's meant to be a rectangle - name it Rectangle :) — Jon Clements
– Jon Clements, Commented Aug 13, 2014 at 11:35

fredtantini · Accepted Answer · 2014-08-13 11:09:15Z

1

I don't know what you really are trying to do in your check function but the following works ok for me:

>>> class Square():
...      def __init__(self,length, width):
...          self.length=length
...          self.width=width
...      @property
...      def area(self):
...          return(self.length*self.width)
...
>>> a=Square(2,3)
>>> a.length
2
>>> a.area
6
>>> a.length=4
>>> a.length
4
>>> a.area
12
>>> for i in range(4):
...   a.length = i
...   print a.area
...
0
3
6
9

edited Aug 13, 2014 at 11:09

answered Aug 13, 2014 at 11:01

fredtantini

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3 Comments

jack Over a year ago

i know this works but i am trying to alter the outcome of class, by function 'check' output.

fredtantini Over a year ago

Well, the title of your question mislead me, and I find the content not clear. Could you provide a minimal working example?

glglgl Over a year ago

@jack Whether you do that "directly" or from within a function, it should make no difference.

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