Python Dictionary comprehension for a list of dictionaries

Question

I want to create a dictionary from the following list

[{'fips': '01001', 'state': 'AL', 'name': 'Autauga County'}, {'fips': '20005', 'state': 'KS', 'name': 'Atchison County'}, {'fips': '47145', 'state': 'TN', 'name': 'Roane County'}]

The result should have the name as the key and 'United States' as the value.

eg:

{'Autauga County': 'United States', 'Atchison County' : 'United States',  'Roane County' : 'United States'}

I can do this with a couple of for loops but i want to learn how to do it using Dictionary Comprehensions.

Answer 1

in_list = [{'fips': '01001', 'state': 'AL', 'name': 'Autauga County'}, 
           {'fips': '20005', 'state': 'KS', 'name': 'Atchison County'},
           {'fips': '47145', 'state': 'TN', 'name': 'Roane County'}]

out_dict = {x['name']: 'United States' for x in in_list if 'name' in x}

Some notes for learning:

• Comprehensions are only for Python 2.7 onwards
• Dictionary comprehensions are very similar to list comprehensions except with curly braces {} (and keys)
• In case you didn't know, you can also add more complicated control-flow after the for loop in a comprehension such as [x for x in some_list if (cond)]

For completeness, if you can't use comprehensions, try this

out_dict = {}

for dict_item in in_list:
    if not isinstance(dict_item, dict):
        continue

    if 'name' in dict_item:
        in_name = dict_item['name']
        out_dict[in_name] = 'United States'

As mentioned in the comments, for Python 2.6 you can replace the {k: v for k,v in iterator} with:

dict((k,v) for k,v in iterator)

You can read more about this in this question

Happy Coding!

Answer 2

Here's a little solution working for both python2.7.x and python 3.x:

data = [
    {'fips': '01001', 'state': 'AL', 'name': 'Autauga County'},
    {'fips': '20005', 'state': 'KS', 'name': 'Atchison County'},
    {'fips': '47145', 'state': 'TN', 'name': 'Roane County'},
    {'fips': 'xxx', 'state': 'yyy'}
]

output = {item['name']: 'United States' for item in data if 'name' in item}
print(output)

Answer 3

The loop/generator version is:

location_list = [{'fips': '01001', 'state': 'AL', 'name': 'Autauga County'},
        {'fips': '20005', 'state': 'KS', 'name': 'Atchison County'},
        {'fips': '47145', 'state': 'TN', 'name': 'Roane County'}]
location_dict = {location['name']:'United States' for location in location_list}

Output:

{'Autauga County': 'United States', 'Roane County': 'United States',
 'Atchison County': 'United States'}

If you search on Stackoverflow for dictionary comprehension, solutions using the { } generator expression start to show up: Python Dictionary Comprehension

Answer 4

That should do the trick for you

states_dict = [{'fips': '01001', 'state': 'AL', 'name': 'Autauga County'}, {'fips': '20005', 'state': 'KS', 'name': 'Atchison County'}, {'fips': '47145', 'state': 'TN', 'name': 'Roane County'}]

{states_dict[i]['name']:'United States' for i, elem in enumerate(states_dict)}