# List / list – how to find the next element

An example of a python function iterating over a list in which we access the next element.

Using the function **zip** you can get the previous object. However, we will go with a simple enumeration.

Function principle:

— First we sort the list in the reverse direction.

– At the first iteration, we assign the value

– At the second iteration, we will be able to work with this value

– At the end, sort again

def calculate_prev_diff_balance(data):

data.reverse()

data.reverse()

prev = None

for x in data:

if prev_sum:

x[‘new_sum’] = x[‘sum’] -prev_sum

prev_sum = x[‘sum’]

data.reverse()

return data