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?

Answer 1

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.

Answer 2

Use set difference

>>> 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.