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Find item in list in Python

Find item in list in Python

David Y.

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The Problem

How can I find an item in a Python list?

The Solution

To check whether a list contains an item, we can use the Python in operator:

Click to Copy
products = ["Apples", "Pears", "Oranges"]

if "Apples" in products:
    print("Apples for sale!")

To return the index of a given item in a list, see this answer.

If we don’t want to find a specific item, but a list of items that fulfill some condition (for example, all the odd numbers in a list) we can use a list comprehension, as below:

Click to Copy
my_list = [1, 4, 7, 8, 3] 
odd_numbers = [n for n in my_list if n%2]

print(odd_numbers) # will print [1, 7, 3]

The list comprehension in odd_numbers will go through my_list and construct a new list of every item it finds that has a nonzero modulo 2 (that is, produces a remainder when divided by two).

If we want only the first item from our list that satisfies our condition, we change our list comprehension into a call to the Python next function.

Click to Copy
my_list = [1, 4, 7, 8, 3] 
odd_number = next(n for n in my_list if n%2)

print(odd_number) # will print 1

If next does not find a value, it will throw a StopIteration exception. To prevent it from doing so, we can provide a default value to return as an additional argument.

Click to Copy
my_list = [4, 8] 
odd_number = next((n for n in my_list if n%2), None)

print(odd_number) # will print None
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