# Reduce with Python and Clojure

I was just playing around writing an annuity calculator function. Here is my first version:

def calculate_annuity(years, interest=0, addition_per_year=0, starting_amount=0):
result = []
running_total = starting_amount
for year in range(years+1):
result.append(running_total)
running_total = (running_total + addition_per_year) * (1 + interest)
return result


Here is a 2nd version, written using reduce instead of a loop:

def calculate_annuity2(years, interest=0, addition_per_year=0, starting_amount=0):
return reduce(lambda result,addition: result + [(result[-1] + addition) * (1 + interest)],
[addition_per_year] * years, [starting_amount])


And here is a version in Clojure (basically a direct translation of the Python one:

(defn annuity [years interest addition_per_year init]
(reduce
#(conj %1 (* (+ (last %1) %2) (+ 1 interest)))
[starting_amount]
(for [i (range years)] addition_per_year)))


Here are some example use cases:

; Find investment returns by year for a \$1000 investment ...