Python __delattr__() Magic Method

Python’s magic method __delattr__() implements the built-in delattr() function that takes an object and an attribute name as arguments and removes the attribute from the object.

We call this a “Dunder Method” for Double Underscore Method” (also called “magic method”). To get a list of all dunder methods with explanation, check out our dunder cheat sheet article on this blog.

Syntax and Example

object.__delattr__(object, attr)

Let’s have a look at an example where you override the __delattr__ magic method of a custom class Car to change the speed attribute value to 42 instead of deleting it:

class Car:
    def __init__(self):
        self.speed = 100

    def __delattr__(self, attr):
        self.speed = 42

# Create object
porsche = Car()


print(porsche.speed)
# 100

delattr(porsche, 'speed')

print(porsche.speed)
# 42

Note that if you wouldn’t have overridden the __delattr__() magic method, Python would’ve removed the speed attribute which would’ve led to an error. You can see this scenario next in our recap on the built-in delattr() function.

Background delattr()

Python’s built-in delattr() function takes an object and an attribute name as arguments and removes the attribute from the object.

The call delattr(object, 'attribute') is semantically identical to del object.attribute.

Before we dive into a practical example of the delattr() function, feel free to watch my explainer video here:

Let’s dive into an example next.

First, create a Car object with one attribute speed.

# Define class with one attribute
class Car:
    def __init__(self):
        self.speed = 100


# Create object
porsche = Car()

Next, print the attribute speed:

# What's the value for attribute speed?
print(porsche.speed)
# 100

Now, use delattr(porsche, speed) to remove the attribute speed from the object porsche.

# Remove the attribute speed from porsche
delattr(porsche, 'speed')

After removing the attribute, it cannot be accessed anymore:

# Does this still work?
print(porsche.speed)
# No:
'''
Traceback (most recent call last):
  File "C:\Users\xcent\Desktop\Finxter\Blog\HowToConvertBooleanToStringPython\code.py", line 18, in <module>
    print(porsche.speed)
AttributeError: 'Car' object has no attribute 'speed'
'''

References:

Where to Go From Here?

Enough theory. Let’s get some practice!

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