Best 2 Ways To Create A Python List With Identical Elements: One-Liners

How can you create a list with identical elements in it with Python?

There are two ways to create a list with identical elements in Python. One method is fairly straightforward and easy to remember, whereas the other involves the itertools library.

The one I apply the most in my Python coding is the method that uses the asterisk operator to a list containing the item I want to replicate. The other method uses the resources and techniques of a library with a function that is difficult to forget: itertools.repeat()

Here’s a quick example demonstrating both approaches, with the first being the approach I apply the most:

>>> my_list = ['hello'] * 5
>>> print(my_list)
['hello', 'hello', 'hello', 'hello', 'hello']

The other approach is using the itertools library which needs to be imported and the repeat() function:

>>> from itertools import repeat
>>> my_list = list(repeat('hello', 5))
>>> print(my_list)
['hello', 'hello', 'hello', 'hello', 'hello']

Both approaches are easy to remember, the only aspect I tend to forget with the itertools is to wrap the repeat() function with the list() constructor as the repeat() function returns an iterator (not a list).

Here’s more detail on each approach below.

Understanding Python Lists

Definition of a Python List

In Python, a list is a mutable, ordered collection of elements, which may have different data types such as integers, strings, or even other lists.

Lists use square brackets [] to enclose their elements, with each element separated by commas.

Why Lists are Used

Lists are essential data structures in Python programming because they provide a way to store multiple related items in an organised manner.

With lists, you can group, arrange and organise data, making it easier to perform tasks like searching, sorting, or iterating through the elements. Lists can help us store data that may change in quantity or value over time, providing flexibility and efficiency in our code.

Creating a Simple List

Creating a list in Python is straightforward. You just need to enclose the elements in square brackets and separate them with commas.

Here’s an example of how to create a simple list:

fruits = ['apple', 'banana', 'cherry']

This list contains three string elements – apple, banana, and cherry.

You can create lists with different data types or even combine data types, like this:

mixed_list = [1, 'hello', 3.14, ['a', 'b', 'c']]

Elements in a Python list

In a Python list, elements are individual items that make up the list. They can be of any data type, including strings, integers, floats, or even other lists. Elements are enclosed in square brackets and separated by commas.

Accessing and manipulating list elements

To access elements in a list, you can use indexing with square brackets.

Python uses zero-based indexing, meaning the first element is at index 0 .

You can also use negative indexing to access elements from the end of the list.

Additionally, you can use slicing to access multiple elements at once.

Manipulating list elements includes modifying their values, appending new items, or removing existing elements.

Some common methods for manipulating list elements are append() , insert() , remove() , and pop() .

Importance of identical elements in programming

Lists with identical elements can be useful in various programming tasks. They can be used for initialising variables with default values, filling in missing data, or creating matrices and tables with fixed values. Understanding how to create and use lists with identical elements allows you to work more efficiently and think more strategically about solving problems in Python.

Creating a list of identical elements

Using the asterisk (*) operator

In Python, the asterisk (*) operator is commonly used for arithmetic operations such as multiplication.

However, it can also be used to duplicate a list’s elements. When creating a list of identical elements, the asterisk operator can be used together with the number of repetitions needed for the element.

For example, let’s say you wanted to create a list with 5 identical elements, all containing the string 'hello' :

>>> identical_elements_list = ['hello'] * 5
>>> print(identical_elements_list)
['hello', 'hello', 'hello', 'hello', 'hello']

Using the itertools.repeat() method

The Python standard library includes a module called itertools which offers a collection of tools for working with iterable data sets, such as lists. One of the functions in this module is repeat() .

This function creates an iterator that returns the same value a specified number of times.

To create a list of identical elements using itertools.repeat() and to use the same example of having 5 identical elements in a list, with the string 'hello' would be as follows:

>>> from itertools import repeat
>>> identical_elements_iterator = repeat('hello', 5)
>>> identical_elements_list = list(identical_elements_iterator)
>>> print(identical_elements_list)
['hello', 'hello', 'hello', 'hello', 'hello']

As you can see, the itertools library approach requires importing the library using the repeat() function and then converting it to a list() . Many steps required, but nonetheless another approach.

Creating Python List With Identical Elements: Summary

Both the asterisk operator * and the itertools.repeat() method effectively generates lists containing identical elements.

When choosing between the two, consider the following:

  • The asterisk operator is simpler and more concise, making it a great choice for small lists and quick operations.
  • On the other hand, the itertools.repeat() method is more flexible and memory-efficient, as it generates an iterator rather than creating an actual list. It might be the better choice for large data sets or when memory usage is a concern.
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Ryan Sheehy
Ryan has been dabbling in code since the late '90s when he cut his teeth exploring VBA in Excel. Having his eyes opened with the potential of automating repetitive tasks, he expanded to Python and then moved over to scripting languages such as HTML, CSS, Javascript and PHP.