dict comprehension

main.js

const foo = {
    x: {a: 10, b: 1},
    y: {a: 20, b: 2},
    z: {a: 30, b: 3}
}

const bar = Object.entries(foo).reduce((acc, [key, value]) => ({...acc, [key]: value.a}), {});

console.log(bar);  // { x: 10, y: 20, z: 30 }

main.py

foo = {
    'x': {'a': 10, 'b': 1},
    'y': {'a': 20, 'b': 2},
    'z': {'a': 30, 'b': 3}
}

bar = {key: value['a'] for key, value in foo.items()}

print(bar)  # {'x': 10, 'y': 20, 'z': 30}