Check If Value Exists in Python List of Objects

In Python, checking if a specific value exists in a list of objects is a common task. There are several methods to achieve this, and in this article, we will explore five generally used methods with simple code examples. Each method provides a different approach to checking for the existence of a value in a list of objects.

To Check If Value Exists in Python List Of Objects

Below, are the ways To Check If Value Exists In Python List Of Objects in Python.

• Using a For Loop
• Using filter Function
• Using lambda() Function

Create a List of Objects

In this example, the below code defines a `Person` class with attributes for name and age. An array `people` is then created, containing instances of the `Person` class, and the type of the `people` array is printed, resulting in “<class ‘list’>”.

Python3

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

people = [Person("Alice", 25), Person("Bob", 30), Person("Charlie", 22)]
print(type(people))

Output

<class 'list'>

Check If Value Exists In Python Using a For Loop

In this example, below code iterates through the list of people and checks if there is a person with age 30. If found, it prints “A person with age 30 exists in the list,” otherwise, it prints “No person with age 30 found in the list.”

Python3

# Check if a person with age 30 exists in the list
target_age = 30
found = False

for person in people:
    if person.age == target_age:
        found = True
        break

if found:
    print(f"A person with age {target_age} exists in the list.")
else:
    print(f"No person with age {target_age} found in the list.")

Output

A person with age 30 exists in the list.

Check If Value Exists In Python Using filter() Function

In this example, below code employs the `filter` function with a lambda expression to create an iterable of people with age 30. The `any` function then determines if there’s at least one person in the filtered list, and it prints either “A person with age 30 exists in the list.”

Python3

# Using the filter function to check for the existence of a person with age 30
target_age = 30
filtered_people = filter(lambda person: person.age == target_age, people)
found = any(filtered_people)

if found:
    print(f"A person with age {target_age} exists in the list.")
else:
    print(f"No person with age {target_age} found in the list.")

Output

A person with age 30 exists in the list.

Check If Value Exists In Python Using lambda() Function

In this example, below code utilizes the `map` function with a lambda expression to create an iterable of boolean values indicating whether each person’s age is 30. The `any` function then checks if at least one of these values is True, and it prints either “A person with age 30 exists in the list.”

Python3

# Using the map and any functions to check for the existence of a person with age 30
target_age = 30
found = any(map(lambda person: person.age == target_age, people))

if found:
    print(f"A person with age {target_age} exists in the list.")
else:
    print(f"No person with age {target_age} found in the list.")

Output

A person with age 30 exists in the list.