`AttributeError`

AttributeError is a built-in exception that occurs when you attempt to access a method or attribute that isn’t defined for the object in question.

You should handle this exception to ensure your code doesn’t crash. Catching an AttributeError allows you to provide a graceful degradation or alternative solution when users try to access an attribute that’s missing.

`AttributeError` Practical Use Cases

Accessing a method or attribute that doesn’t exist in a class or module
Using the wrong attribute name due to a typo
Accessing an attribute that was supposed to be dynamically added but hasn’t been initialized yet
Attempting to access attributes on a NoneType object due to uninitialized or improperly assigned variables

`AttributeError` Examples

An example of when the exception appears:

Python
      
        
      
    
>>> class Dog:
...     def bark(self):
...         print("Woof!")
...

>>> dog = Dog()
>>> dog.meow()
Traceback (most recent call last):
    ...
AttributeError: 'Dog' object has no attribute 'meow'

An example of how to handle the exception:

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>>> class Dog:
...     def bark(self):
...         print("Woof!")
...
>>> dog = Dog()

>>> try:
...     dog.meow()
... except AttributeError:
...     print("The Dog class doesn't have a 'meow' method.")
...
The Dog class doesn't have a 'meow' method.

Every Python object will raise an AttributeError when you attempt to access a non-existent attribute on it. When you need to implement custom logic, then you can edit .__getattr__() accordingly before raising the error manually:

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>>> class CustomObject:
...     def __getattr__(self, name):
...         # Write to logs
...         raise AttributeError(f"No '{name}' here.")
...

>>> obj = CustomObject()
>>> obj.missing_attribute
Traceback (most recent call last):
    ...
AttributeError: No 'missing_attribute' here.

You could also provide fallback mechanisms for the lookup before raising the AttributeError. Raising it manually also allows you to customize the error message.

`AttributeError` How to Fix It

For example, say that you have a Pen class with a .color attribute:

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>>> class Pen:
...     def __init__(self, color):
...         self.color = color
...

>>> pen = Pen("black")
>>> pen.color
'black'
>>> pen.colour
Traceback (most recent call last):
    ...
AttributeError: 'Pen' object has no attribute 'colour'.
⮑ Did you mean: 'color'?

The class works correctly with .color but fails with .colour. To fix the above code, you could customize the attribute lookup in .__getattr__() before raising AttributeError manually:

Python
      
    
class Pen:
    def __init__(self, color):
        self._color = color

    def __getattr__(self, name):
        if name in ["color", "colour"]:
            return self._color
        else:
            raise AttributeError(f"'{type(self).__name__}' object has no attribute '{name}'")

    def __setattr__(self, name, value):
        if name in ["color", "colour"]:
            super().__setattr__("_color", value)
        else:
            super().__setattr__(name, value)

With these edits to Pen, you users can now access the ._color attribute with both .color and .colour:

Python
      
        
      
    
>>> pen = Pen("black")
>>> pen.color
'black'
>>> pen.colour
'black'
>>> pen.stroke
Traceback (most recent call last):
    ...
AttributeError: 'Pen' object has no attribute 'stroke'

At the same time, the class still raises an AttributeError when you try to access a non-existent attribute.

Note that you need to manually raise AttributeError in .__getattr__() if you overwrite the default implementation with your custom logic. Otherwise, you break the default behavior of raising an AttributeError when looking up a non-existent attribute.

Tutorial

Python's Built-in Exceptions: A Walkthrough With Examples

In this tutorial, you'll get to know some of the most commonly used built-in exceptions in Python. You'll learn when these exceptions can appear in your code and how to handle them. Finally, you'll learn how to raise some of these exceptions in your code.

intermediate python

For additional information on related topics, take a look at the following resources: