Check if a value exists in a List of Dictionaries in Python

# Table of Contents

1. Check if a value exists in a List of Dictionaries in Python
2. Check if a value doesn't exist in a list of dictionaries
3. Get a list of all of the values for a given key
4. Check if a value exists in a List of Dictionaries using a for loop
5. Get the index of the matching dictionary in the list
6. Check if a value exists in a List of Dictionaries using filter
7. Check if a value exists in a List of Dictionaries using map

# Check if a value exists in a List of Dictionaries in Python

To check if a value exists in a list of dictionaries:

1. Use a generator expression to iterate over the list.
2. Access the given key in each dictionary and compare it to the value.
3. Pass the result to the any() function.

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list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

if any(
    dictionary.get('name') == 'bobby'
    for dictionary in list_of_dicts
):
    # 👇️ this runs
    print('A dictionary with the specified value exists')

The first example checks if a value exists in a list of dictionaries.

The second checks if a value does not exist in a list of dictionaries.

We used a generator expression to iterate over the list.

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list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

if any(
    dictionary['name'] == 'bobby'
    for dictionary in list_of_dicts
):
    # 👇️ this runs
    print('A dictionary with the specified value exists')

On each iteration, we access the name key and compare its value to a specific string.

The any function takes an iterable as an argument and returns True if any element in the iterable is truthy.

# Check if a value doesn't exist in a list of dictionaries

If you need to check if a value doesn't exist in a list of dictionaries, negate the call to any().

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list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

if not any(dictionary.get('name') == 'bobby'
           for dictionary in list_of_dicts):
    print('None of the dictionaries contain the specified value')

The not operator flips the result, so the if block is only run if the value doesn't exist in any of the dictionaries in the list.

The dict.get() method returns the value for the given key if the key is in the dictionary, otherwise a default value is returned.

The method takes the following 2 parameters:

# Get a list of all of the values for a given key

If you need to get a list of all of the values for a given key, use a list comprehension.

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list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

name_values = [
    dictionary['name'] for dictionary in list_of_dicts
]
print(name_values)  # 👉️ ['alice', 'bobby', 'carl']

print('bobby' in name_values)  # 👉️ True
print('another' in name_values)  # 👉️ False

We use a list comprehension to iterate over the list.

On each iteration, we access a specific key in the current dictionary and return the corresponding value.

Alternatively, you can use a for loop.

# Check if a value exists in a List of Dictionaries using a for loop

This is a three-step process:

1. Use a for loop to iterate over the list.
2. Access the given key in each dictionary and compare it to the value.
3. If you find a matching dictionary, exit the for loop.

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list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

value_exists = False

for dictionary in list_of_dicts:
    if dictionary.get('name') == 'bobby':
        value_exists = True
        # 👇️ {'id': 2, 'name': 'bobby', 'salary': 101}
        print(dictionary)

        break

We used a for loop to iterate over the list.

On each iteration, we check if the current dictionary has a name key with a specific value.

If the condition is met, we set the value_exists variable to True and exit the for loop.

The break statement breaks out of the innermost enclosing for or while loop.

# Get the index of the matching dictionary in the list

If you need to get the index of the matching dictionary in the list, use the enumerate() function.

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list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

value_exists = False

for index, dictionary in enumerate(list_of_dicts):
    if dictionary.get('name') == 'bobby':
        value_exists = True
        # 👇️ {'id': 2, 'name': 'bobby', 'salary': 101}
        print(dictionary)

        print(index)  # 👉️ 1

        break

We used the enumerate() function to get access to the index of the current iteration.

The enumerate() function takes an iterable and returns an enumerate object containing tuples where the first element is the index and the second is the corresponding item.

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my_list = ['bobby', 'hadz', 'com']

for index, item in enumerate(my_list):
    print(index, item)  # 👉️ 0 bobby, 1 hadz, 2 com

# Check if a value exists in a List of Dictionaries using filter

You can also use the filter() function to check if a value exists in a list of dictionaries.

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list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

matching_dicts = list(
    filter(
        lambda x: x.get('name') == 'bobby',
        list_of_dicts
    )
)

# [{'id': 2, 'name': 'bobby', 'salary': 101}]
print(matching_dicts)


if len(matching_dicts) > 0:
    print('The value exists in the list of dictionaries')

The filter() function takes a function and an iterable as arguments and constructs an iterator from the elements of the iterable for which the function returns a truthy value.

The lambda function we passed to filter() gets called with each dictionary from the list.

The function gets the name attribute of the dictionary and compares it to the given value.

If the condition is met, the dictionary is included in the filter object.

The last step is to check if the length of the variable is greater than 0.

If it is, then at least one dictionary has the specified value.

# Check if a value exists in a List of Dictionaries using map

You can also use the map() function to check if a value exists in a list of dictionaries.

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from operator import itemgetter

list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

if 'bobby' in map(itemgetter('name'), list_of_dicts):
    # 👇️ this runs
    print('The value is in the dictionary')
else:
    print('The value is NOT in the dictionary')

The map() function takes a function and an iterable as arguments and calls the function with each item of the iterable.

The operator.itemgetter() class returns a callable object that fetches the items at the specified indices or keys.

For example, x = itemgetter('name') and then calling x(my_dict), returns my_dict['name'].

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from operator import itemgetter

list_of_dicts = [
    {'id': 1, 'name': 'alice', 'salary': 100},
    {'id': 2, 'name': 'bobby', 'salary': 101},
    {'id': 3, 'name': 'carl', 'salary': 102},
]

# 👇️ ['alice', 'bobby', 'carl']
print(list(map(itemgetter('name'), list_of_dicts)))

The last step is to use the in operator to check if the given value is contained in the list.

I've also written an article on how to filter a list of dictionaries.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Remove a Dictionary from a List of Dictionaries in Python
• Remove duplicates from a List of Dictionaries in Python
• Check if a Value exists in a Two-dimensional List in Python
• Check if multiple Values are in a List in Python
• How to merge two JSON objects in Python
• How to destructure Dictionaries and Lists in Python