python 26 lines · 7 steps

A rolling average over a fixed window

Maintain a running sum alongside a bounded deque so each new value yields an average in constant time.

Explained by highlit
Intermediate sliding-window running-sum deque amortized-o1
1from collections import deque
2 
3 
4class RollingAverage:
5 def __init__(self, window):
6 if window <= 0:
7 raise ValueError("window must be positive")
8 self.window = window
9 self._values = deque(maxlen=window)
10 self._total = 0.0
11 
12 def add(self, value):
13 if len(self._values) == self.window:
14 self._total -= self._values[0]
15 self._values.append(value)
16 self._total += value
17 return self.average
18 
19 @property
20 def average(self):
21 if not self._values:
22 return None
23 return self._total / len(self._values)
24 
25 def __len__(self):
26 return len(self._values)
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Tracking a running total lets you avoid re-summing the window on every update.
  2. 2A deque with maxlen automatically discards old items, but you must subtract them from your total first.
  3. 3Exposing the average as a property keeps the computed value consistent with the stored state.

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