UDF for Exponential moving average in Pig Latin

Today I faced with the fact that there's no native way to calculate moving average in Pig.

For example:

A = {(5, 1), (2, 2), (7, 3), (4, 4)}
And we need to calculate EMA of first field, with weight of second field. alpha=0.5.

ema(A) = (5*1 + 2*0.5 + 7*0.25 + 4*0.125) / (1 + 0.5 + 0.25 + 0.125) = 4.4

In Pig and Python UDF it will be like this:

REGISTER 'python_udf.py' USING jython AS myfuncs;

B = GROUP A ALL;
C = FOREACH times {
    GENERATE A as src,
             myfuncs.EMA(A, 1, 3, 0.5) as ema;
}

DUMP C;

UDF:

@outputSchema("value:double")
def EMA(D, weight_field, wmax, alpha):
    """
    Calculates exponential moving average
    note: weights are reversed!
    """
    weights = [x for x in range(1, wmax+1)]
    weights_values = {}
    wv = 1.0
    for w in weights:
        weights_values[w] = wv
        wv *= alpha
    denom = sum(weights_values.values())
    numer = 0.0
    for weight in weights:
        numer += sum(1 for x in D if x[weight_field] == weight)*weights_values[weight]
    return numer/denom

Pretty straightforward, but it works. If you know more elegant way, please share it!