Subtracting Lists: Computing the Difference

Lists in Python can contain various elements. To perform mathematical operations on lists, such as subtraction, we employ specific methods or techniques. Let's explore how to subtract one list from another.

Using List Comprehension for Element-by-Element Subtraction

One approach is to utilize a list comprehension, which iterates over the first list and computes the difference while preserving the original order:

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

Subtracting Sets for Faster Computations

If maintaining the ordering of elements is not crucial, a set-based approach offers faster computations:

list(set(x) - set(y))

Overriding sub for List Subtractions

To enable list subtraction using the infix "-" operator, we can override the __sub__ method of a class inheriting from list:

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])

Example usage:

x = MyList(1, 2, 3, 4)
y = MyList(2, 5, 2)
z = x - y    # z becomes a MyList object containing the difference