How do you calculate the difference between two lists in Python?

Computing List Difference in Python

When working with lists in Python, it's often necessary to compute the difference between two lists. The difference between two lists involves identifying elements that are present in one list but not in the other.

To compute the difference between two lists, you can utilize the set data structure. Sets are unordered collections of unique elements. By converting the lists to sets, you can easily identify their differences using set operations.

If the order of the elements in the result does not matter, you can use the set difference operation:

<code class="python">set_A = set([1, 2, 3, 4])
set_B = set([2, 5])

diff_A_minus_B = set_A - set_B
diff_B_minus_A = set_B - set_A

print(diff_A_minus_B)  # {1, 3, 4}
print(diff_B_minus_A)  # {5}</code>

This approach returns a set containing the elements that are present in one set but not in the other.

Alternatively, if you want to preserve the order of the elements, you can use the list comprehension approach:

<code class="python">list_A = [1, 2, 3, 4]
list_B = [2, 5]

diff_A_minus_B = [element for element in list_A if element not in list_B]
diff_B_minus_A = [element for element in list_B if element not in list_A]

print(diff_A_minus_B)  # [1, 3, 4]
print(diff_B_minus_A)  # [5]</code>

This approach constructs a new list containing the elements that are unique to each input list.

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