Moving average

A sensor sends readings one at a time, and you want the average of the last k readings after each one arrives (or of all readings so far, while there are fewer than k). A deque with maxlen=k keeps exactly the last k, dropping the oldest by itself.

Write moving_averages(readings, k) that returns a list with the average after each reading, rounded to two decimal places.

moving_averages([10, 20, 30, 40], 2)  ->  [10.0, 15.0, 25.0, 35.0]
moving_averages([3, 6, 9], 5)         ->  [3.0, 4.5, 6.0]

from collections import deque

def moving_averages(readings, k):
    ...