How to apply successive methods on object

user_7580912 0
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I have defined an object that will have an argument. Then I have created 3 methods as:

  1. do_it1 will add 10 on value of the object
  2. do_it2 will add 20 on value of the object
  3. do_it3 could accept an argument then it should add 30 plus its input argument on what's applied on.i.e. to what is on the left side.

Here's what I did

class MyClass():

def __init__(self,object_value):
    self.object_value = object_value

def do_it1 (self):
    return self.object_value + 10

def do_it2 (self):
    return self.object_value + 20

def do_it3 (self,input_number):
    self.input_number = input_number
    return  + 30 + self.input_number

here is the output

MyClass(5).do_it1()

returns 15 which is correct

MyClass(4).do_it2()

returns 24 which is correct

MyClass(4).do_it2().do_it3(6)

returns AttributeError: 'int' object has no attribute 'do_it3' while I was expecting 60 as 4 + 20 + 30 + 6

MyClass(1).do_it1().do_it2().do_it3(9)

returns AttributeError: 'int' object has no attribute 'do_it2' while I was expecting 1 + 10 + 20 + 30 + 9 = 70

How I could apply a method on top of method(s) in same class

oop python
4 Answers

You need to return self (or a copy of it, via import copy, copy.copy(self) or similar) for this to work. The accrued value has to be accessed via the object_value property.

In code:

class MyClass():
    def __init__(self,object_value):
        self.object_value = object_value

    def do_it1(self):
        self.object_value += 10
        return self

    def do_it2(self):
        self.object_value += 20
        return self

    def do_it3(self, input_number):
        self.input_number = input_number
        self.object_value += 30 + self.input_number
        return self


MyClass(4).do_it2().do_it3(6).object_value
# 60
MyClass(1).do_it1().do_it2().do_it3(9).object_value
# 70

(method do_it3() may or may not do what you want, your code is invalid so I just guessed, but it is not too relevant)

user_52183540

In this statement you call init which creates an object of MyClass self.object_value = 5 and then you call do_it1() of it

MyClass(5).do_it1()

In the second one you do the same thing, but you create an object with self.object_value = 4 and then you call.do_it2()

MyClass(4).do_it2()

In the last one it returns you an error because you create the object MyClass with self.object_value = 4, then you call do_it2() which returns an Int value, so you will have Int.do_it3(6) in the end, which raises an error because the int object has no method do_it(3). All of the return value of MyClass(4).do_it2() is an int and then you call a method that is not a method of the return object.

MyClass(4).do_it2().do_it3(6)

I hope this helps. Let me know if you did not understand.

user_123545860

As these methods return ints, you can only call int methods on their results.

Your invocation MyClass(4).do_it2().do_it3(6) is equivalent to 24.do_it3(6), which does not make much sense.

user_75313530

For MyClass(4).do_it2().do_it3(6) the problem is that do_it2() returns an integer; to that integer you are applying the method do_it3(), but the integer class does not have any method call do_it3(). You could try:

MyClass(4).do_it3(6 + MyClass(4).do_it2())
user_115960810
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