Question

Describe three different ways of making a copy of a list that don't involve the list function.

Short answer

Use slicing, list comprehension, or the list's `copy()` method.

Step-by-step solution

Using Slicing

One way to make a copy of a list in Python without using the list function is to use the slicing technique. You can create a copy by slicing the entire list as follows: ```python list_copy = original_list[:] ``` This creates a shallow copy of the list by taking all elements from start to end.

Using List Comprehension

Another method to copy a list is by using list comprehension. This involves creating a new list by iterating over the original list and adding each element to the new list: ```python list_copy = [item for item in original_list] ``` This statement evaluates each element in the `original_list` and includes it in the new `list_copy`, effectively creating a shallow copy.

Using the copy Method

A third way to copy a list is to use the `copy` method available for list objects in Python. This method creates a shallow copy of the list: ```python list_copy = original_list.copy() ``` The `copy` method is specifically designed for lists and avoids the use of the `list()` constructor.

Key concepts

Slicing in Python

Slicing in Python is a powerful technique that allows you to extract a portion of a list by specifying the start and end indices. When you use slicing to copy a list, you create a new list that contains all the elements of the original list. This technique is both simple and quick. Here's how you can make a copy of a list using slicing:

• If you want to copy an entire list, you can use `original_list[:]`. This will effectively create a new list that starts from the first element and goes to the last, inclusive.
• The slicing operation ensures that each element is copied, but it's important to remember that this creates a shallow copy. This means if the original list contains other lists, the copied list will reference the same inner lists.

Slicing is intuitive and often favored for its clean and readable syntax. It can be very handy when you need a straightforward method to duplicate lists. Remember, the `[:]` slice is a shorthand to tell Python to include every item in the list.

List Comprehension

List comprehension is a concise way to create lists in Python. It allows you to generate a new list by iterating over an existing iterable, like a list or a range of numbers. This method can also be used to copy a list by simply iterating through each element of the original list:

• The syntax for list comprehension is generally `[expression for item in iterable]`. When copying a list, the expression is often just the `item`, so it looks like `[item for item in original_list]`.
• List comprehension provides the opportunity to include additional conditions, although when copying a list, you might not need those. For simple copying purposes, it replicates the behavior of the list, creating another list with the same elements.

While list comprehension is a bit more verbose than slicing, it is similarly straightforward and also results in a shallow copy. It's particularly useful if you want to copy and possibly filter a list at the same time.

Python copy method

The `copy` method is a built-in feature for Python lists, providing a designated way to make a copy of a list. This method is quite direct and very readable, perfect for scenarios where you want to express the intent of copying explicitly:

• Using `original_list.copy()` returns a new list, which is a shallow copy of the `original_list`. You don't need to pass any arguments to this method.
• Like slicing and list comprehension, the `copy` method will result in a shallow copy. This means any changes made to the copied list will not affect the original, and vice versa, unless the list contains mutable objects like other lists.

The advantage of using the `copy` method is clarity. It's explicitly clear that you're duplicating the list, which can improve code understandability for others reading it. For many Python developers, utilizing this method is a preferred and modern approach for duplicating lists.