Sort subset of dictionary keys

Question

How do i sort the following list B that is a subset of dictionary A, based on A's values?

A = {1: 10, 2:20, 3: 15, 4: 1}
B = [1, 3, 4]

My solution should be

B = [4, 1, 3]

since

A[4] < A[1] < A[3]

Answer 1

Use A.get as key

A = {1: 10, 2:20, 3: 15, 4: 1}
B = [1, 3, 4]

>>> sorted(B, key=A.get)
[4, 1, 3]

Notice that you can set a default value as argument for the .get method, such that, if a given key doesn't exist in your dict, you can set a position yourself (eg last position or first). For example:

B = [1, 3, 4, 11]
>>> sorted(B, key=lambda k: A.get(k, -1))
[11, 4, 1, 3]

>>> sorted(B, key=lambda k: A.get(k, float('inf')))
[4, 1, 3, 11]

Or, as highlighted by @jpp,

>>> sorted(B, key=A.__getitem__)

if you prefer a KeyError to be raised if referenced key doesn't exist.