Question

I have a Python Dictionary like:

Mydict = {‘a’: {‘y’: 1, ‘x’: 5}, ‘b’: {‘y’: 10, ‘x’: 8}}

Is there any quick way to access the values corresponding to the key: ‘x’, which in this case is a second level key, regardless of the first level key?

I know it can be done using a for loop like:

mylist=[]
for k in Mydict.keys():
    mylist.append(Mydict[k]['x'])

But is there any quick one line method for it?

Answer 1

Using list-comprehension:

mylist = [v['x'] for v in Mydict.values()]

Since you do not need the outer keys, you just iterate over the inner dicts, and get the desired 'x' value.

Note: This will only work if each inner dict has an 'x' key, to be sure, and to minimize errors, you can do this:

mylist = [v.get('x', None) for v in Mydict.values()]

This will function the same, only if there is no 'x' key in the dictionary, it will return None instead of a KeyError exception.

For timing, and to see which method is best, look at the answer by Thorsten Kranz