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

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.

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

@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()

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