How to Check If Something Is Not In A Python List

To check if something is not in a Python list, you can use the not in operator. This operator allows you to check if a value is not present in a list. It returns True if the value is not found in the list, and False otherwise.

Here are two ways to check if something is not in a Python list:

1. Using the not in operator

You can use the not in operator to check if a value is not present in a list. The syntax is as follows:

value not in list

Here, value is the value you want to check for, and list is the list in which you want to search for the value.

Example:

numbers = [1, 2, 3, 4, 5]

# Check if 6 is not in the list
if 6 not in numbers:
    print("6 is not in the list")

# Check if 3 is not in the list
if 3 not in numbers:
    print("3 is not in the list")

Output:

6 is not in the list

In the example above, the first if statement is true because 6 is not present in the numbers list. The second if statement is false because 3 is present in the numbers list.

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2. Using the in operator with the not keyword

Alternatively, you can use the in operator with the not keyword to achieve the same result. The syntax is as follows:

not value in list

Example:

numbers = [1, 2, 3, 4, 5]

# Check if 6 is not in the list
if not 6 in numbers:
    print("6 is not in the list")

# Check if 3 is not in the list
if not 3 in numbers:
    print("3 is not in the list")

Output:

6 is not in the list

In this example, the output is the same as the previous example. The first if statement is true because 6 is not present in the numbers list, and the second if statement is false because 3 is present in the numbers list.

These are the two ways to check if something is not in a Python list. You can choose the one that you find more readable or intuitive.

Best Practices

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When checking if something is not in a Python list, keep the following best practices in mind:

- Use the not in operator or the in operator with the not keyword, as they provide a concise and readable way to perform the check.

- If you need to check for multiple values, you can use a loop or list comprehension to iterate over the values and perform the check for each value.

- Consider using sets instead of lists if you have a large number of values to check, as sets offer faster membership tests compared to lists.

These best practices can help you write clean and efficient code when checking if something is not in a Python list.