Question

What will the following code display? numbers1 = [1, 2, 3] numbers2 = [10, 20, 30] numbers3 = numbers1 + numbers2 print(numbers1) print(numbers2) print(numbers3)

Short answer

Answer: The output will be as follows: [1, 2, 3] [10, 20, 30] [1, 2, 3, 10, 20, 30]

Step-by-step solution

Initialize lists

The code initializes two lists, numbers1 and numbers2, as follows: numbers1 = [1, 2, 3] numbers2 = [10, 20, 30]

Combine the two lists

The code combines the two lists using the "+" operator, creating a new list named numbers3: numbers3 = numbers1 + numbers2 In this step, numbers1 and numbers2 remain unchanged, and the new list numbers3 is created as the result of their concatenation: [1, 2, 3, 10, 20, 30].

Print the lists

The code prints the three lists (numbers1, numbers2, and numbers3) in that order: print(numbers1) print(numbers2) print(numbers3) The output will be as follows: [1, 2, 3] [10, 20, 30] [1, 2, 3, 10, 20, 30]

Key concepts

List Initialization in Python

In Python, initializing a list means creating a new list and assigning it with initial values. This is typically done by enclosing a comma-separated sequence of values within square brackets. For example, when we write numbers1 = [1, 2, 3], we are declaring a list named numbers1 and initializing it with the integers 1, 2, and 3.

Lists are versatile and can contain items of different data types, including numbers, strings, and even other lists. This flexibility makes them exceptionally useful in various programming scenarios, from holding a series of numbers to managing complex data structures. List initialization is the foundation upon which list manipulation, such as concatenation and sorting, is built.

Understanding how to initialize lists properly is a critical step when learning to code in Python because many problems involve creating and modifying lists. When initializing a list, ensure that you do not accidentally overwrite an existing list if you intend to preserve its contents.

Combining Lists with the '+' Operator

Combining, or concatenating, lists in Python can be done using the '+' operator. This operator takes two lists and creates a new list that includes all the elements of the first list followed by all elements of the second list. In the exercise, after initializing numbers1 and numbers2, we combine them by writing numbers3 = numbers1 + numbers2.

Upon utilizing the '+' operator, numbers3 now holds a new list composed of the items from numbers1 and then numbers2, resulting in [1, 2, 3, 10, 20, 30]. Importantly, neither numbers1 nor numbers2 are modified by this operation; a new list is simply created from their elements.

Remember, directly combining lists with the '+' operator creates a new list in memory. If you've large lists or performance is a concern, consider using the .extend() method or list comprehensions for more efficient concatenation.

Using the Print Statement to Display Lists

The print statement in Python is used to display the contents of variables, including lists, to the standard output (usually the screen). When you execute print(numbers1), it outputs the list's contents in a readable format, enclosed in square brackets and separated by commas.

The exercise demonstrates printing the contents of the initialized and combined lists. It displays the following output:
[1, 2, 3]
[10, 20, 30]
[1, 2, 3, 10, 20, 30]

Using the print statement is fundamental for debugging and for providing users with output. Always ensure output is presented in a clear manner to facilitate understanding. For more complex data types, you might need to iterate through the items or use formatting techniques to present them in a more structured or visually appealing format.