Question

What will the following code display? \\[\begin{array}{l}\text { numbers }=[1,2,3,4,5] \\ \text { numbers }[2]=99\end{array}\\] print (numbers)

Short answer

Solution: The output will be the updated list, which is [1, 2, 99, 4, 5].

Step-by-step solution

Understand the Code

Before we begin, let's understand the given code. The code defines a list called 'numbers' with 5 integers in it. Then, it assigns a new integer value of 99 at the 2nd index position in the list (Python uses zero-based indexing). Finally, it prints the 'numbers' list.

Apply the Assignment Operation

Next, let's apply the assignment operation to the list. The code line "numbers[2] = 99" assigns the value 99 to the element located at the 2nd index of the list, which is the 3rd element. So, the original list: \([1, 2, 3, 4, 5]\) will now have the new values as: \([1, 2, 99, 4, 5]\)

Print the List

Now that the list has been updated with the new value, the final command "print(numbers)" should display the list as it is, with the new values. The output will be: \([1, 2, 99, 4, 5]\)

Key concepts

Indexing

In Python, lists are a powerful feature allowing you to store and manage collections of data. To interact with lists, understanding "indexing" is crucial. Indexing allows you to access individual elements in a list by referring to their position number. By default, indexing in Python starts at 0. This means the index of the first element in a list is 0, the second is 1, and so on. For example, in the list `numbers = [1, 2, 3, 4, 5]`, accessing the element with `numbers[2]` retrieves the third element, which is `3` because:

• `numbers[0]` returns `1`
• `numbers[1]` returns `2`
• `numbers[2]` returns `3`
• `numbers[3]` returns `4`
• `numbers[4]` returns `5`

New users must remember that Python uses zero-based indexing, which may differ from one-based indexing used in some other programming languages. This zero-based approach can prevent off-by-one errors in programming.

Assignment Operation

In Python programming, modifying list elements is straightforward thanks to the assignment operation. This is the process of setting or changing the value of an element in a list. The beauty of lists lies in their mutability, which allows you to change their contents without altering the entire list structure. Given the initial list `numbers = [1, 2, 3, 4, 5]`, suppose you want to replace the third element (i.e., `3`) with `99`. You achieve this by using the assignment operation as follows: `numbers[2] = 99`. Here, `numbers[2]` refers to the element we want to modify, and `99` is the new value we're assigning. After this operation, the updated list becomes:

• `numbers = [1, 2, 99, 4, 5]`

This method is efficient and essential for any situation where dynamic data manipulation is required. Always ensure you are referencing the correct index to prevent unintentional data replacement.

Output Display

Displaying the result of your code execution is essential to verify the list modifications. Once you've applied any changes to your list, such as a reassignment of elements, the next step is to display the output so you can observe the impact of your code. In Python, the `print()` function is used to output data. After modifying the list, you can use this function to display the current contents of the list. From our example, after changing the value at index `2`, you execute `print(numbers)`. This command will output the list, showing the updated values:

• Output: `[1, 2, 99, 4, 5]`

This visual confirmation is vital in programming to ensure your operations have succeeded and that your data reflects the desired state. Hence, always use print statements not just to debug, but also to solidify your understanding of list manipulations as you learn.