Getting a list of values from a list of dicts

Question

I have a list of dicts like this:

[{\'value\': \'apple\', \'blah\': 2}, 
 {\'value\': \'banana\', \'blah\': 3} , 
 {\'value\': \'cars\', \'blah\': 4}]
         


        

Answer 1

For a very simple case like this, a comprehension, as in Ismail Badawi's answer is definitely the way to go.

But when things get more complicated, and you need to start writing multi-clause or nested comprehensions with complex expressions in them, it's worth looking into other alternatives. There are a few different (quasi-)standard ways to specify XPath-style searches on nested dict-and-list structures, such as JSONPath, DPath, and KVC. And there are nice libraries on PyPI for them.

Here's an example with the library named dpath, showing how it can simplify something just a bit more complicated:

>>> dd = {
...     'fruits': [{'value': 'apple', 'blah': 2}, {'value': 'banana', 'blah': 3}],
...     'vehicles': [{'value': 'cars', 'blah':4}]}

>>> {key: [{'value': d['value']} for d in value] for key, value in dd.items()}
{'fruits': [{'value': 'apple'}, {'value': 'banana'}],
 'vehicles': [{'value': 'cars'}]}

>>> dpath.util.search(dd, '*/*/value')
{'fruits': [{'value': 'apple'}, {'value': 'banana'}],
 'vehicles': [{'value': 'cars'}]}

Or, using jsonpath-ng:

>>> [d['value'] for key, value in dd.items() for d in value]
['apple', 'banana', 'cars']
>>> [m.value for m in jsonpath_ng.parse('*.[*].value').find(dd)]
['apple', 'banana', 'cars']

This one may not look quite as simple at first glance, because find returns match objects, which include all kinds of things besides just the matched value, such as a path directly to each item. But for more complex expressions, being able to specify a path like '*.[*].value' instead of a comprehension clause for each * can make a big difference. Plus, JSONPath is a language-agnostic specification, and there are even online testers that can be very handy for debugging.