Computing with lists¶

Here we will practice using of lists and combining the techniques we have learned so far.

This task is a combination of the tasks we have done so far. In the first part of the assignment we copy the positive numbers from the tuple into the list, and in the second part we apply the function min to the list of positive numbers.

We mentioned that the functions min, max, sum, len can be applied to different collections, and we have shown this with examples of tuple, range and string (except the sum of the elements of a string). We now see that the min function also accepts a list as its argument. The same holds to the functions max, sum, len.

The first part of the assignment requires that we count the number of times each number appears in the input data. To solve this part of the task, we create the list num_failures of 10 elements (that are initially zero), in which each element corresponds to one machine and counts its failures.

num_failures = [0] * 10
for machine in failures:
    num_failures[machine] += 1

After that, we print out for each machine how many failures it had. We use the range here because we want to print machine sequence number and number of failures for each machine:

for i in range(10):
    print('Machine', i, 'failed', num_failures[i], 'times.')

The second part of the assignment asks us to print the machine numbers that had never failed. These are machines whose number of failures is zero. We go through the list num_failures again and insert indices of elements equal to zero in the new list, named not_failed:

not_failed = []
for i in range(10):
    if num_failures[i] == 0:
        not_failed.append(i)

Finally, we print the items of the list not_failed.

print('Machines that did not break down:')
for machine in not_failed:
    print(machine)

Here’s what the whole program looks like:

The assignment asks for each number 0 to 7 to count how many times that number appears among the given numbers. The missing part in the script is very similar to counting the failures in the given example.

If you complete the task correctly, the program should print number 3, because that number appears most often in the data.

There are two ways to solve this task. One is to extract small amounts to a separate list and apply the sum function to that list. Another way is to gradually build up the sum, as we did in the lesson on counting and summing.