# Python list subtraction operation

### Question

I want to do something similar to this:

``````>>> x = [1,2,3,4,5,6,7,8,9,0]
>>> x
[1, 2, 3, 4, 5, 6, 7, 8, 9, 0]
>>> y = [1,3,5,7,9]
>>> y
[1, 3, 5, 7, 9]
>>> y - x   # (should return [2,4,6,8,0])
``````

But this is not supported by python lists What is the best way of doing it?

1
193
9/26/2012 11:19:02 PM

Use a list comprehension:

``````[item for item in x if item not in y]
``````

If you want to use the `-` infix syntax, you can just do:

``````class MyList(list):
def __init__(self, *args):
super(MyList, self).__init__(args)

def __sub__(self, other):
return self.__class__(*[item for item in self if item not in other])
``````

you can then use it like:

``````x = MyList(1, 2, 3, 4)
y = MyList(2, 5, 2)
z = x - y
``````

But if you don't absolutely need list properties (for example, ordering), just use sets as the other answers recommend.

279
1/26/2012 11:57:02 PM

``````>>> z = list(set(x) - set(y))
>>> z
[0, 8, 2, 4, 6]
``````

Or you might just have x and y be sets so you don't have to do any conversions.