import math
from collections import Counter
base = {
    'shannon' : 2.,
    'natural' : math.exp(1),
    'hartley' : 10.,
    'somerandbase'   : 256.
    }
def eta(data, unit):
    if len(data) <= 1:
        return 0
    counts = Counter()
    for d in data:
        counts[d] += 1
        ent = 0
        probs = [float(c) / len(data) for c in counts.values()]
        for p in probs:
            if p > 0.:
                ent -= p * math.log(p, base[unit])
    return ent
for i in base:
    print ( eta("abcde",i))
    print ( eta("lllll",i))

python foo.py
2.321928094887362
0.0
1.6094379124341005
0.0
0.6989700043360187
0.0
0.2902410118609203
0.0