Retrieving items from keys using conditions from multiple dictionaries in a list

Question

I am trying to retrieve the item from a key in select dictionaries within a list of dictionaries, where selection of the dictionary is conditional on the value of the item against multiple other keys present in the dictionaries.

E.g. For list of dictionaries, d:

d = [{a:'2.1', z:'apple', aa:'banana'}, {a:'3.6', z:'cherry', aa:'peach'}, {a:'4.7', z:'apple', aa:'banana'}, {a:'1.6', z:'apple', aa:'orange'}]

I am interested in retrieving the item against 'a' for the last dictionary in the list where 'z':'apple' and 'aa':'banana' are satisfied conditions i.e. get the item against key 'a' from d[-2] in the above example.

Is there some simple code to do this?

I have tried:

1. Python: get a dict from a list based on something inside the dict - but not sure how to extend this to be conditional on the items against multiple keys inside the dictionaries.

2. Slicing a dictionary - but not sure how to add the conditional aspect using Python syntax.

I expect the solution involves some sort of dictionary comprehension, but am relatively new to Python.

Any help appreciated.

Answer 1

You can use list comprehension to filter list of dictionaries by condition and take the last dictionary from satisfied cases:

dicts = [{'a':'2.1', 'z':'apple', 'aa':'banana'}, {'a':'3.6', 'z':'cherry', 'aa':'peach'}, 
         {'a':'4.7', 'z':'apple', 'aa':'banana'}, {'a':'1.6', 'z':'apple', 'aa':'orange'}]

filtered_list = [elem for elem in dicts if elem.get('z') == 'apple' and elem.get('aa') == 'banana']
if filtered_list:
    result = filtered_list[-1]
else:
    result = None
    print("There's no satisfied dictionary.")
print(result)
# {'a': '4.7', 'z': 'apple', 'aa': 'banana'}
print(result['a'])
# 4.7

Answer 2

Iterate the reversed list, and break as soon as you find a dict satisfying the conditions:

dicts = [{'a':'2.1', 'z':'apple', 'aa':'banana'}, {'a':'3.6', 'z':'cherry', 'aa':'peach'}, 
         {'a':'4.7', 'z':'apple', 'aa':'banana'}, {'a':'1.6', 'z':'apple', 'aa':'orange'}]

for d in reversed(dicts):
    if d['z'] == 'apple' and d['aa'] == 'banana':
        break

print(d)
# {'a': '4.7', 'z': 'apple', 'aa': 'banana'}