Utilizing Control Flow Structures in Python

Currently, the take_first function will raise an error if it receives an empty list of todos, but we'd like to handle that differently. Our doctests show that we should instead be returning (None, todos) if todos is empty. There is more than one way that we could go about doing this:

1. Use a conditional statement to see if todos is empty right away. If it is, then return (None, todos).
2. Use a try statement, and if an error is raised return (None, todos).

For simplicity's sake let's use a conditional, instead of error handling, as control flow:

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'}]
    >>> todos = []
    >>> take_first(todos)
    (None, [])
    """
    if todos:
        todo = todos.pop(0)
        return (todo, todos)
    else:
        return (None, todos)

The original version of sum_points takes two todo dictionaries and returns the sum of their point values. But that's not very useful. For us to make this work for us, we're going to modify the function so that it will take a list of todo dictionaries and sum all of the point values. We can do this easily, using a for loop and an accumulator:

def sum_points(todos):
    """
    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'},
    ... {'name': 'Task 3', 'body': 'Third task', 'points': '5'}]
    >>> sum_points(todos)
    10
    """
    total = 0
    for todo in todos:
        total += int(todo['points'])
    return total