Python’s magic method
__delitem__(self, key) implements the deletion of
self[key]. So, if you call
del self[key], Python will call
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 Minimal Example
Let’s have a look at an example where you override the
__delitem__ magic method of a custom class
class HelloWorld: def __delitem__(self, key): print('hello world', key) hi = HelloWorld() del hi # hello world 42 del hi['wide web'] # hello world wide web
This code shows several interesting things:
- You use the
delkeyword to initiate the
- You use
del obj[key]to call
- You can pass arbitrary keys into it.
However, this is just a dummy example, let’s have a look at a full example implementing all methods
__delitem__ that together play together beautifully to implement a collection-like custom data type.
In the following example, you create a custom list-like type that overrides the
class MyList: def __init__(self, lst): self.lst = lst def __getitem__(self, key): print('__getitem__', key) return self.lst[key] def __setitem__(self, key, value): print('__setitem__', key, value) self.lst[key] = value def __delitem__(self, key): print('__delitem__', key) del self.lst[key]
Each time you add a new element, get an element, or delete an element from your custom list, it prints the respective information so you see what happens.
my = MyList(['alice', 'bob', 'carl']) print(my) # __getitem__ 1 # bob
Note how Python first calls the print statement within the
__getitem__ output and key
1 and then returns the element
my itself, puts it into the
print(...) statement which results in the output
Next, you overwrite the value of the second list element with index 1:
my = '42' print(my) # __setitem__ 1 42 # __getitem__ 1 # 42
You can see from the print output
__setitem__ 1 42 that
__setitem__ was called with key
1 and value
Next, you delete an element with the expression
del my print(my) # carl
Where to Go From Here?
Enough theory. Let’s get some practice!
Coders get paid six figures and more because they can solve problems more effectively using machine intelligence and automation.
To become more successful in coding, solve more real problems for real people. That’s how you polish the skills you really need in practice. After all, what’s the use of learning theory that nobody ever needs?
You build high-value coding skills by working on practical coding projects!
Do you want to stop learning with toy projects and focus on practical code projects that earn you money and solve real problems for people?
🚀 If your answer is YES!, consider becoming a Python freelance developer! It’s the best way of approaching the task of improving your Python skills—even if you are a complete beginner.
If you just want to learn about the freelancing opportunity, feel free to watch my free webinar “How to Build Your High-Income Skill Python” and learn how I grew my coding business online and how you can, too—from the comfort of your own home.
While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
To help students reach higher levels of Python success, he founded the programming education website Finxter.com that has taught exponential skills to millions of coders worldwide. He’s the author of the best-selling programming books Python One-Liners (NoStarch 2020), The Art of Clean Code (NoStarch 2022), and The Book of Dash (NoStarch 2022). Chris also coauthored the Coffee Break Python series of self-published books. He’s a computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.