Completing tasks

Update status with complete_task.

Completing tasks (complete_task)

Let us write a complete_task function to complete tasks. It takes an index and updates the task at that index:

def complete_task(index):
    if 0 <= index < len(tasks):
        tasks[index] = tasks[index] + " [done]"

This appends " [done]" to the task's title. With if we check that the index is valid; so we do not go out of the list.

Why is index checking important?

Without index checking, a call like tasks[10] raises IndexError; this crashes the program. Checking with if makes the program run safely:

if 0 <= index < len(tasks):
    # safe operation

This is a good software habit. It protects the code against wrong inputs and prevents the user from seeing error messages.

Exercise Add the complete_task function

Define a function called complete_task that takes an index parameter. In the body check with if 0 <= index < len(tasks): and mark with tasks[index] = tasks[index] + " [done]". Call complete_task(0), then list with list_tasks().

Show example solution

def complete_task(index):
    if 0 <= index < len(tasks):
        tasks[index] = tasks[index] + " [done]"
complete_task(0)
list_tasks()

Test yourself

What does 0 <= index < len(tasks) check?
- Is index positive
- Is index integer
- Is index large
- Is index in the list
Show answer

Is index in the list — This condition checks that index is in the list.

Complete the complete_task body

def complete_task(index):
    if 0 <= index < ____(tasks):
        tasks[index] = tasks[index] + " [done]"

Show answer

def complete_task(index):
    if 0 <= index < len(tasks):
        tasks[index] = tasks[index] + " [done]"

Match the completing parts

index

Parameter
0 <= index < len

Check
tasks[index] =

Assignment
complete_task(0)

Call

Next lesson: Putting it together

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