Question

What will the following code display? numbers = [1, 2, 3, 4, 5] my_list = numbers[:] print(my_list)

Short answer

Answer: [1, 2, 3, 4, 5]

Step-by-step solution

Reviewing list declaration

Create a list called 'numbers' which contains integers 1, 2, 3, 4, 5.

Understanding list slicing

List slicing is the process of extracting specific parts of a list by using indices and colon syntax. In the provided code, the slicing operation is performed with empty indices on both sides of the colon, which implies that the entire list will be copied into the new list 'my_list'.

Slicing and creating a new list

By slicing 'numbers' with empty indices on both sides of the colon, the entire list is copied and a new list called 'my_list' is created. This operation is functional, fast and, commonly referred to as cloning a list.

Print the output

The last step is to print the 'my_list'. Since 'my_list' is a copy of 'numbers', it will contain the same elements as 'numbers'. So, the output will be: [1, 2, 3, 4, 5].

Key concepts

List declaration in Python

Creating lists in Python is a fundamental skill, as lists are versatile and widely used to store collections of data. To declare a list, you simply assign a series of values enclosed in square brackets to a variable. For example:

fruits = ['apple', 'banana', 'cherry']
Here, fruits is a list that contains three string elements. Lists can hold any type of object: numbers, strings, and even other lists. They can also be empty:empty_list = []
Understanding how to create and utilize lists is crucial for handling data efficiently in Python.

List copying via slicing

Slicing a list not only allows you to access a subsection of the list, but it can also be used to make a full copy. The syntax my_list[:] is used to create a clone of my_list. It works by not specifying a start or end index, which defaults to the beginning and end of the list respectively. This technique is handy for when you need to work with a copy of the list and leave the original untouched.
For instance, the following code:
original = [1, 2, 3, 4]copy = original[:]
results in copy being an exact replica of original but as a different object in memory. This ensures that any modifications to copy do not affect original.

Understanding Python list indices

In Python, each item in a list has an assigned index value, starting from zero. This index is used to access and manipulate individual list elements. For example, in the list letters = ['a', 'b', 'c', 'd'], letters[0] will return 'a'. Conversely, Python also supports negative indexing. letters[-1] would return 'd' as it refers to the last item.

Indices are also essential for slicing. By specifying a start index and an optional end index, you can extract subsections of the list: letters[1:3] yields ['b', 'c']. Remember that the end index is not inclusive. Understanding how indices work makes it easier to perform more complex operations like reversing a list using slicing: letters[::-1] or accessing specific elements.

Python list operations

Once a list is created, Python provides a plethora of operations to modify or interrogate it. Here are some frequently used list operations:

• Adding items: Use .append() for a single item or .extend() for multiple items.
• Inserting: The .insert() method lets you add an element at a specific index.
• Removing: Elements can be removed by value with .remove() or by index with del.
• Sorting: You can sort a list in place with .sort() method.
• Reversing: Use .reverse() or slicing my_list[::-1] to reverse the order of elements.

These operations enable dynamic and flexible manipulation of list data structures, making them an indispensable tool for any Python programmer.