Add the col column to self.data, add the numerical value of f to self.data[], and use the shift() method to shift the row by the value of lag.
Add the value stored in col to self.cols data with the append() method.
In self.data['vol'], add a vol column to store the following
In self.data['return'].rolling() method, execute the window function in the return column. The period is self.window. Then, we calculate the standard deviation in the .std() method.
The calculation method executes the window function on the return column with self.data['return'].rolling(self.window). The argument is the value of self.window. The mean() method is executed on the result to calculate the average value.