import math

# returns a simple lowpass filter function, based on the specified parameters
def filterA(alpha, initial):
    def f(x):
        f.prev = x * (1.0 - alpha) + f.prev * alpha
        return f.prev
    f.prev = initial
    return f

# create some test signal
testSignal = [math.sin(0.25 * x) for x in range(20)]

# see the result of applying two of these filters, chained together, on the
# test signal
print(map(filterA(alpha=0.95, initial=7.5), map(filterA(alpha=0.99, initial=-1.5), testSignal)))