# Python Check if Item Exists in a List with in Operator

> Check if a Python list contains an item using the in operator for single lookups, or convert to a set for faster membership testing across large collections

**URL:** https://sentry.io/answers/fastest-way-to-check-if-a-list-contains-an-item-in-python/

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## The Problem

Using Python, what is the fastest way to check if an item is present in a list?

## The Solution

This depends on the size of the list and the number of items to check for. When checking for a single item in a list, the fastest way is to use Python's `in` operator:

```python
my_list = [1, 2, 3, 4, 5]

if 4 in my_list:
    print("4 is present.")
```

If we're checking for multiple items in a large, unordered list, it can be faster to convert the list and the items to [`set`s](https://docs.python.org/3/tutorial/datastructures.html#sets) before performing the check.

```python
import random

my_list = list(range(1,10001))      # list of number 1 to 10000
random.shuffle(my_list)             # put my_list in a random order
items_to_find = list(range(1,1001)) # find the numbers 1 to 1000

my_list_set = set(my_list)
items_to_find_set = set(items_to_find)
for item in items_to_find_set.intersection(my_list_set):
    print(f"{item} is present.")
```

Performance can vary at lower scales and for different lists. When searching for a single item in a list, `in` should be sufficient; when searching for common items between two very long lists with thousands of items, `set` conversion is probably the way to go.

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*Source: [sentry.io/answers/fastest-way-to-check-if-a-list-contains-an-item-in-python/](https://sentry.io/answers/fastest-way-to-check-if-a-list-contains-an-item-in-python/)*