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:
  def __init__(self, window):
      if window <= 0:
          raise ValueError("window must be positive")
      self.window = window
      self._values = deque(maxlen=window)
      self._total = 0.0
11 
  def add(self, value):
      if len(self._values) == self.window:
          self._total -= self._values[0]
      self._values.append(value)
      self._total += value
      return self.average
18 
  @property
  def average(self):
      if not self._values:
          return None
      return self._total / len(self._values)
24 
  def __len__(self):
      return len(self._values)

01 / 01

STEP 01

Walkthrough

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Three takeaways

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

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