Update exponential_moving_average.py

Author: cclauss

financial/exponential_moving_average.py

@@ -1,5 +1,5 @@
 """
-    Calculate the exponential moving average (EMA) on the series of numbers.
+    Calculate the exponential moving average (EMA) on the series of stock prices.
     Wikipedia Reference: https://en.wikipedia.org/wiki/Exponential_smoothing
     https://www.investopedia.com/terms/e/ema.asp#toc-what-is-an-exponential
     -moving-average-ema
@@ -13,30 +13,30 @@
 
 
 def exponential_moving_average(
-    series: Iterator[float], window_size: int
+    stock_prices: Iterator[float], window_size: int
 ) -> Iterator[float]:
     """
-    Returns the generator which generates exponential moving average of the given
-    series
-    >>> list(exponential_moving_average(iter([2, 5, 3, 8.2, 6, 9, 10]), 3))
-    [2.0, 3.5, 3.25, 5.725, 5.8625, 7.43125, 8.715625]
+    Yields exponential moving averages of the given stock prices.
+    >>> tuple(exponential_moving_average(iter([2, 5, 3, 8.2, 6, 9, 10]), 3))
+    (2, 3.5, 3.25, 5.725, 5.8625, 7.43125, 8.715625)
 
-    :param series: Generator which generates numbers
-    :param window_size: Window size for calculating average (window_size > 0)
-    :return: Returns generator of which returns exponentially averaged numbers
+    :param stock_prices: A stream of stock prices
+    :param window_size: The number of stock prices that will trigger a new calculation
+                        of the exponential average (window_size > 0)
+    :return: Yields a sequence of exponential moving averages
 
     Formula:
 
     st = alpha * xt + (1 - alpha) * st_prev
 
     Where,
     st : Exponential moving average at timestamp t
-    xt : Datapoint in series at timestamp t
+    xt : stock price in from the stock prices at timestamp t
     st_prev : Exponential moving average at timestamp t-1
     alpha : 2/(1 + window_size) - smoothing factor
 
     Exponential moving average (EMA) is a rule of thumb technique for
-    smoothing time series data using the exponential window function.
+    smoothing time series data using an exponential window function.
     """
 
     if window_size <= 0:
@@ -45,41 +45,29 @@ def exponential_moving_average(
     # Calculating smoothing factor
     alpha = 2 / (1 + window_size)
 
-    # Defining timestamp t
-    timestamp = 0
-
     # Exponential average at timestamp t
-    exponential_average = 0.0
+    moving_average = 0.0
 
-    for datapoint in series:
-        if timestamp <= window_size:
+    for i, stock_price in enumerate(stock_prices):
+        if i <= window_size:
             # Assigning simple moving average till the window_size for the first time
             # is reached
-            exponential_average = (
-                float(datapoint)
-                if timestamp == 0
-                else (exponential_average + datapoint) * 0.5
-            )
+            moving_average = (moving_average + stock_price) * 0.5 if i else stock_price
         else:
             # Calculating exponential moving average based on current timestamp data
             # point and previous exponential average value
-            exponential_average = (alpha * datapoint) + (
-                (1 - alpha) * exponential_average
-            )
-        timestamp += 1
-        yield exponential_average
+            moving_average = (alpha * stock_price) + ((1 - alpha) * moving_average)
+        yield moving_average
 
 
 if __name__ == "__main__":
     import doctest
 
     doctest.testmod()
 
-    test_series = [2, 5, 3, 8.2, 6, 9, 10]
-    test_window_size = 3
-    result = exponential_moving_average(
-        series=iter(test_series), window_size=test_window_size
-    )
-    print("Test series: ", test_series)
-    print("Window size: ", test_window_size)
-    print("Result: ", list(result))
+    stock_prices = [2.0, 5, 3, 8.2, 6, 9, 10]
+    window_size = 3
+    result = tuple(exponential_moving_average(iter(stock_prices), window_size))
+    print(f"{stock_prices = }")
+    print(f"{window_size = }")
+    print(f"{result = }")