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Python Python Basics (2015) Python Data Types Lists

Dave Masom
Dave Masom
9,584 Points
Posted by Dave Masom
Dave Masom
9,584 Points

Remove all instances of a value from a list

Is there a way to remove all instances of a value in a list? For example, if I have: my_list = [1, 2, 3, 3, 3]

my_list.remove(3) results in my_list = [1, 2, 3, 3].

Can I call a method to remove all of the 3s in my_list?

john larson
john larson
16,594 Points

Hi Dave, glad to help. It took me a few minutes to figure it out and when I got it I was pleasantly surprised.

john larson
john larson
16,594 Points

Seth, it looks like yours is creating a new list out of only the desired characters? Kinda like the opposite of what I did?

2 Answers

john larson
john larson
16,594 Points

This seemed to work. Though I'm sure there are more graceful ways to do it. I'll be curious what someone else will suggest.

for num in my_list:
    my_list.remove(3)
Seth Kroger
Seth Kroger
56,414 Points
Seth Kroger
Seth Kroger
56,414 Points 
my_list = [x for x in my_list if x != 3]

works too

Dave Masom
Dave Masom
9,584 Points
Dave Masom
Dave Masom
9,584 Points

Thanks John, it worked for me too. And I understood your solution as well - even better!

John Schaub
John Schaub
5,167 Points
John Schaub
John Schaub
5,167 Points

I tried both methods and Seth's ended with the results intended and John's left me with a syntax error! not sure what I did wrong?

my_list = [54321, 3, 3, 3]
my_list
[54321, 3, 3, 3]
for num in my_list: my_list.remove(3)
... my_list
File "<stdin>", line 2
my_list
^
SyntaxError: invalid syntax

john larson
john larson
16,594 Points

I didn't get a syntax error, but it left one 3 when running the code on you're list. Seths code is cooler anyway :D Ok, I ran my code in the python shell and got that syntax error, but it did remove all the 3's. So I would have to add some more code to clean it up. Seths is still better.

ryan smith
ryan smith
687 Points

What does x for x in my_list mean? I didn't understand your solution.

Seth Kroger
Seth Kroger
56,414 Points
Seth Kroger
Seth Kroger
56,414 Points

It's called a list comprehension. Comprehensions are kinda unique to Python (it is the only major language to have them). It's a bit like a for loop but it basically means "make a new list but running through the items of the old list and checking if they meet a condition". You can check out this workshop for more: https://teamtreehouse.com/library/python-comprehensions