# scipy.signal lfilter

def discount(x, gamma): """ Compute discounted sum of future values out[i] = in[i] + gamma * in[i+1] + gamma^2 * in[i+2] + ... """ return signal.lfilter([1], [1, -gamma], x[::-1], axis=0)[::-1]

**Here is what the above code is Doing:**

1. The first line is a function definition. It takes two arguments, x and gamma, and returns a value.

2. The second line is a docstring. It’s a special kind of comment that describes what the function does.

3. The third line is a call to the lfilter function from the scipy.signal module.

4. The fourth line reverses the array.

5. The fifth line reverses the array again.