What are the Methods to Compute List Differences in Python?

How to Compute List Differences

To determine the difference between two lists, x and y, there are several approaches available in Python.

Using List Comprehensions

To preserve the order of elements in x, a list comprehension can be employed:

<code class="python">[item for item in x if item not in y]</code>

This expression creates a new list, including only those elements from x that are not present in y.

Using Set Differences

If ordering is not crucial, a set difference can be used:

<code class="python">list(set(x) - set(y))</code>

This approach converts both x and y into sets, computes the difference, and then converts the result back into a list.

Overriding Class Methods

To enable infix subtraction syntax (e.g., x - y), you can override the sub method in a class that inherits from list:

<code class="python">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])

x = MyList(1, 2, 3, 4)
y = MyList(2, 5, 2)
z = x - y  # Infix subtraction syntax</code>

In this scenario, z will contain only the elements in x that are not in y.

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