How to fix Python error: AttributeError: type object X has no attribute Y

Question

I'm creating a practice python file to better understand object oriented programming and I am getting the following error:

AttributeError: type object 'ID' has no attribute 'the_other_number'

I don't really understand why this happens because when I change the variable like below, it works just fine. I only receive an error when I try to use it in an if statement:

ID.the_other_number = 'new_value'

Below is my example code that I am trying to fix, any help is appreciated.

class ID():
   def __init__(self):
       self.other_number()
       pass

   def other_number(self):
       self.the_other_number = 3111

class ID_2():
    def __init__(self):
        self.update_number()

    def update_number(self):
       if ID.the_other_number > 4:
           print(ID.the_other_number)

if __name__ == '__main__':
   ID()
   ID_2()

I was expecting it to understand what variable is equal to and run the if statement correctly. Also, don't try to make sense of the code, I realize the code doesn't make sense, it is simply an example.

The indent of your other_number function in your ID class is off by one. — BoboDarph
– BoboDarph, Commented Feb 5, 2019 at 14:22

Patrick Haugh · Accepted Answer · 2019-02-05 14:29:25Z

2

When you run ID() a new instance of the ID class is created. __init__ calls the other_number method of that instance, which assigns the instance attribute the_other_number. Since you don't save that instance anywhere, by assigning the output of ID(), it's garbage collected immediately. The ID class does not change.

When you run ID_2(), you create an instance of the ID_2 class and run it's __init__ method. That calls the update_number method of that instance, which checks ID._the_other_number. ID has no the_other_number attribute, so an error is raised.

Read the Python tutorial on Classes, and pay special attention to the difference between class objects and instance objects.

answered Feb 5, 2019 at 14:29

Patrick Haugh

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Comments

Eshita Shukla · Accepted Answer · 2019-02-05 14:40:40Z

You are making one mistake: You have to understand that ID is a class, it's not an object

So, if you want to use the function ID.the_other_number, you have to first create an object of ID. So, just add one extra line to your code

class ID():
   def __init__(self):
       self.other_number()
       pass

   def other_number(self):
       self.the_other_number = 3111

class ID_2():
    def __init__(self):
        self.update_number()

    def update_number(self):

        # Create one object of class ID - ID_object
        ID_object = ID()

        # Call the function for ID_object
        if ID_object.the_other_number > 4:
           print(ID_object.the_other_number)

if __name__ == '__main__':
   ID()
   ID_2()

BoboDarph · Accepted Answer · 2019-02-05 14:38:24Z

0

@Patrick Haugh 's answer already explains why your code fails to execute the way you expect it. Absent the issues with indenting, here's how I would modify your code to print the_other_number property of class ID:

class ID():
    def __init__(self):
        self.other_number()

    def other_number(self):
        self.the_other_number = 3111
        return self.the_other_number

class ID_2():
    def __init__(self):
        self.update_number()

    def update_number(self):
        id = ID()
        if id.other_number() > 4:
            print(id.the_other_number)

if __name__ == '__main__':
   ID()
   ID_2()

edited Feb 5, 2019 at 14:38

answered Feb 5, 2019 at 14:31

BoboDarph

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