Fix Python – Check if value already exists within list of dictionaries?

Question

Asked By – AP257

I’ve got a Python list of dictionaries, as follows:

a = [
    {'main_color': 'red', 'second_color':'blue'},
    {'main_color': 'yellow', 'second_color':'green'},
    {'main_color': 'yellow', 'second_color':'blue'},
]

I’d like to check whether a dictionary with a particular key/value already exists in the list, as follows:

// is a dict with 'main_color'='red' in the list already?
// if not: add item

Now we will see solution for issue: Check if value already exists within list of dictionaries?


Answer

Here’s one way to do it:

if not any(d['main_color'] == 'red' for d in a):
    # does not exist

The part in parentheses is a generator expression that returns True for each dictionary that has the key-value pair you are looking for, otherwise False.


If the key could also be missing the above code can give you a KeyError. You can fix this by using get and providing a default value. If you don’t provide a default value, None is returned.

if not any(d.get('main_color', default_value) == 'red' for d in a):
    # does not exist

This question is answered By – Mark Byers

This answer is collected from stackoverflow and reviewed by FixPython community admins, is licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0