Use function to update calculations

Question

I created a function which updates the single list by adding the interest rate.

def first(lst, rate):
 for i in range(len(lst)):
 lst[i] += lst[i] * rate[i]

My question is, how to use this function to update two dimensional list by adding the interest rate?

For example:

lst2 = [[25, 10, 300], [7, 30, 80], [7, 530, 24],[65, 30, 2]]
rate = [0.5, 0.02, 0.15]
>>> for i in lst2:
 print(i)
[37.5, 10.2, 345.0]
[10.5, 30.6, 92.0]
[10.5, 540.6, 27.6]
[97.5, 30.6, 2.3]

My code:

def second(lst2, rate):
 for x in lst2:
 for y in x:
 lst2[x][y] += first(lst2[x][y],rate[x])

Any help will be much appreciated. Thanks

Answer 1

This situation is kind of strange, because you're completely relying on the functions having side-effects instead of returning values. However, here's a solution:

def second(lst2, rate):
 for i in range(len(lst2)):
 first(lst2[i], rate)

Answer 2

Short answer: this is what numpy is for.

import numpy
lst2 = numpy.array( [ ..as above.. ])
rate = numpy.array( [.. as above.. ])
lst_with_interest = lst2 + lst2*rate[numpy.newaxis,:]

Without numpy, it's possible lots of different ways, mostly depending on how general you want the solution to be. A good general way is to write something which does a single dimension, and looks at its parameters to see if the rate is a list or a single number; see the zip() function for dealing with the list case.

Answer 3

Easy way is to say

for i in range(len(lst2)):
 first(lst2[i], rate)

lst2 will then contain [[37.5, 10.2, 345.0], [10.5, 30.6, 92.0], [10.5, 540.6, 27.6], [97.5, 30.6, 2.3]]