Is There a Built-in \'Contains\' Function for Lists in Python?

Does Python Have a Built-in "Contains" Function for Lists?

When working with lists in Python, it's often necessary to check if a particular value exists within the list. For instance, can we determine if [1, 2, 3] contains 2 efficiently?

Solution: Using the "in" Operator

Python provides a concise and efficient way to check for list membership using the in operator. This operator evaluates to True if the specified value exists in the list and False otherwise.

To use the in operator:

<code class="python">if my_item in some_list:
    # Actions to perform if my_item is in some_list</code>

Example:

<code class="python">some_list = [1, 2, 3]

if 2 in some_list:
    print("2 is in the list.")
else:
    print("2 is not in the list.")</code>

Inverses: Checking for Absence

The not in operator can be used to check if a value is not present in a list:

<code class="python">if my_item not in some_list:
    # Actions to perform if my_item is not in some_list</code>

Performance Considerations

The in operation has an O(n) complexity for lists and tuples, where n is the number of elements in the collection. However, for sets and dictionaries, the in operation has an O(1) complexity, indicating much faster lookup times.

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