Access value of a given key in a list of dictionaries-CodePudding

Given a list of dictionaries such as:

list_ = [
        { 'name' : 'date',
          'value': '2021-01-01'
        },
        { 'name' : 'length',
          'value': '500'
        },
        { 'name' : 'server',
          'value': 'g.com'
        },

How can I access the value where the key name == length?

I want to avoid iteration if possible, and just be able to check if the key called 'length' exists, and if so, get its value.

CodePudding user response：

With iteration, and using next, you could do:

list_ = [
    {'name': 'date',
     'value': '2021-01-01'
     },
    {'name': 'length',
     'value': '500'
     },
    {'name': 'server',
     'value': 'g.com'
     }
]

res = next(dic["value"] for dic in list_ if dic.get("name", "") == "length")
print(res)

Output

As an alternative, if the "names" are unique you could build a dictionary to avoid further iterations on list_, as follows:

lookup = {d["name"] : d["value"] for d in list_}
res = lookup["length"]
print(res)

Output

Notice that if you need a second key such as "server", you won't need to iterate, just do:

lookup["server"]  # g.com

CodePudding user response：

It sure is hard to find an element in a list without iterating through it. Thats the first solution I will show:

list(filter(lambda element: element['name'] == 'length', list_))[0]['value']

this will filter through your list only the elements with name 'length', choose the first from that list, then select the 'value' of that element.

Now, if you had a better data structure, you wouldn't have to iterate. In order to create that better data structure, unfortunately, we will have to iterate the list. A list of dicts with "name" and "value" could really just be a single dict where "name" is the key and "value" is the value. To create that dict:

dict_ = {item['name']:item['value'] for item in list_}

then you can just select 'length'

dict_['length']