Solving Problems with Built-in Python Types

Hands-On Lab


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Keith Thompson

DevOps Training Architect II in Content





To be effective with Python we need to be comfortable using the basic data types that Python has to offer. In this Hands-On Lab, we'll be utilizing basic types to fix some failing automated tests, and ensuring that the application is working correctly. By the time we're finished with this hands-on lab we should be more comfortable using the different data types in Python, like strings, numbers, dictionaries, and lists.

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Solving Problems with Built-in Python Types


We've been tasked with building a terminal based todo list application, and it's in its earliest stages. A co-worker has written and documented a few functions that we'll need to implement. By the time we've finished, we should have written implementations for the print_todo, take_first, and sum_points functions within ~/tasker/

Thankfully, our co-worker documented the code using doctests, so we have some automated tests that we can run to ensure that our implementation meets the requirements.

By the time we've implemented these functions, we'll have proven our knowledge of some of Python's built-in types such as strings, integers, dictionaries, lists, and tuples.

Get logged in

Use the credentials and server IP in the hands-on lab overview page to log into the server with SSH.

The file

This is the file we're working with, and it's sitting in the ~/tasker directory, so let's get into the directory and run the file, to see what we're up against:

[user@host]$ cd tasker
[user@host]$ python3.7 -m doctest

This spits out a bunch of errors. The one we're concerned with is up near the beginning of the ouput. The print_todo function exists, but doesn't do anything.

Implement print_todo function

The last line of the print_todo function currently says pass. We need to manually print out a format string (name and body) so let's change that line (in whatever text editor suits our fancy) to read:

print(f"{todo['name']}: {todo['body']}")

The whole section would look like this when we're done:

def print_todo(todo):
    print_todo takes in a todo dictionary and prints it out
    with by separating the `name` from the `body` using a colon (:).

    >>> todo = {'name': 'Example 1', 'body': 'This is a test task', 'points': '3'}
    >>> print_todo(todo)
    Example 1: This is a test task
    print(f"{todo['name']}: {todo['body']}")

If we run the script again, we should see that there are now no failures related to print_todo. We're making progress.

Implement take_first function

The take_first function needs to return 2 objects to us, in the form of the first todo and the remaining todos. We can achieve this by returning a tuple of values, and the pop function on a list should allow us to get the first item. Here's one way that we might implement this function to get the tests passing (changing a simple return line to something that's returning our todo):

def take_first(todos):
    take_first receives a list of todos and removes the first todo
    and returns that todo and the remaining todos in a tuple

    >>> todos = [{'name': 'Example 1', 'body': 'This is a test task', 'points': '3'},
    ... {'name': 'Task 2', 'body': 'Yet another example task', 'points': '2'}]
    >>> todo, todos = take_first(todos)
    >>> todo
    {'name': 'Example 1', 'body': 'This is a test task', 'points': '3'}
    >>> todos
    [{'name': 'Task 2', 'body': 'Yet another example task', 'points': '2'}]
    todo = todos.pop(0)
    return (todo, todos)

Implement sum_points function

The sum_points function needs to receive two todo dictionaries and return the sum of the point values. The doctest shows that the point values will be strings, so we'll need to convert them to be integers before we perform our addition. Here's one way that we could get these tests passing:

def sum_points(todo1, todo2):
    sum_points receives two todo dictionaries and returns the sum of their `point` values.

    >>> todos = [{'name': 'Example 1', 'body': 'This is a test task', 'points': '3'},
    ... {'name': 'Task 2', 'body': 'Yet another example task', 'points': '2'}]
    >>> sum_points(todos[0], todos[1])
    return int(todo1['points']) + int(todo2['points'])


Running python3.7 -m doctest again will return nothing. That's fine. No news is good news. If we wanted verbose output, we could have run python3.7 -m doctest -v and gotten some, but we're good to go either way. We've finished our task. Congratulations!