Nested FOR loops – coding challenge

I am learning python using STEPIK and I am facing this:

I want on every iteration of the inside for loop sum the values of predicted_growth list with the value of cases list, save it in some temporary variable and print it. Click on the link for the full challenge.

This is my code so far:

def predict_cases(cases, predicted_growth):
    print()
    result = []
    for i in range(len(cases)):
        for j in range(len(predicted_growth)):
            result = cases[i] + predicted_growth[j]
            print(result, end = " ")
        print()


cases = [12508, 9969, 310595, 57409]
predicted_growth = [100, 200, 300]

predict_cases(cases, predicted_growth)

This is the output of the function I should be getting:

[12608, 10069, 310695, 57509]
[12808, 10269, 310895, 57709]
[13108, 10569, 311195, 58009]

Instead I am getting this:

12608 12708 12808 
10069 10169 10269 
310695 310795 310895 
57509 57609 57709 

Answer

You can use a loop with an inner list comprehension.

def predict_cases(cases, predicted_growth):
    res = [] # this will hold the results

    for growth_rate in predicted_growth: # outer loop to iterate the growth rate
        prev = res[-1] if res else cases # get the previously computed result, if there is no such result get initial cases (`cases`) as previously computed result
        res.append([growth_rate + i for i in prev]) # list comprehension to add the current growth rate(`growth_rate`) to the previous cases

    for result in res: # iterate through `res` list
        print(result) # print the result

cases = [12508, 9969, 310595, 57409]
predicted_growths = [100, 200, 300]
predict_cases(cases, predicted_growths)

Output

[12608, 10069, 310695, 57509]
[12808, 10269, 310895, 57709]
[13108, 10569, 311195, 58009]