How to create an empty list in Python

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This article covers why creating empty lists is essential and how you will create an empty list in Python. However, like arrays, lists are the collections of items which can be a string, integers or objects. Moreover, lists do not always have to be homogeneous, making it the most potent tool in Python. Items of different datatypes can all be found in a single list. Are you interested in creating an empty list in Python? So if you’re ready to get started, let’s dive into creating Python’s empty lists!

GETTING STARTED WITH Empty ListS

An empty list can be convenient when you want to add things later. However, It’s like having an empty box that you can fill with different items. Empty lists are helpful when you need to add elements to them dynamically at a later time. There are several approaches to creating an empty list in Python:

  • Using square brackets
  • Using the list() function
  • using the * operator: If you already have an empty list and you want to create another one, you can do this by multiplying * operator with an empty list.
  • By using list comprehension: A list can be created using a list comprehension, but with no elements to iterate. It creates an empty list.

Let’s discuss all these approaches in detail along with examples.

Using square brackets

An empty list can be constructed using a pair of square brackets []. This creates a new list object with no elements. Lets see how we can create an empty list using square brackets through an example.

  • Create an empty list, in this case, tagged as ‘string,’ to store the value of the results in it.
  • Take an integer as an input from the user using the input() function which indicates the number of string elements to be stored in that empty list.
  • Now apply a for loop which iterates ‘n‘ times.
  • On every iteration, the loop body will take an input value from the user and add it to the empty list. Moreover, the ‘+‘ operator concatenates each value the user enters each time.
  • Lastly, to print all the values on the display, the print() command invokes.

In this example, we need an empty list so that we can store elements it. We can use the ‘+’ operator and square brackets to concatenate a single-item list to an existing list.

#Creating an empty list 
string = []  
# Taking input from the user
n = int(input("Enter the strings elements: "))

# parsing each string character and adding them to the list
for i in range(n):
    string_input = (input("Enter a string character: "))
    string += [string_input]

# Printing the list
print("lists of strings:", string)
Enter the strings elements: 4
Enter a string character: t
Enter a string character: e
Enter a string character: c
Enter a string character: h
lists of strings: ['t', 'e', 'c', 'h']

Using the list() function

You can also use a built-in list() function with no arguments. This creates an empty list that can be assigned to a variable. The following example demonstrates how to create an empty list using a list() function.

# Creating an empty list for storing number
numbers = list()  

# taking numbers from the user
n = int(input("Enter the number: ")) 

for k in range(n):
    num = float(input("Enter a number: "))
    numbers += [num]

# numbers sorting in ascending order
numbers.sort()

# Printing the  numbers in ascending order
print("Sorted numbers:", numbers)
Enter the number: 5
Enter a number: 6.5
Enter a number: 2.3
Enter a number: 1
Enter a number: 7
Enter a number: 3.9
Sorted numbers: [1.0, 2.3, 3.9, 6.5, 7.0]

In the above example, we have created an empty list using the list() function. Using the input() function, the program takes an input from the user of an integer datatype and stores them in “n” variable. The value inside “n” indicates the number of elements to be inserted into that empty list which in turn indication the number of times the loop is iterated.

The for loop then iterates “n” times and on every iteration, a number is taken as an input from the user converted to floating datatype, and stored in the variable ‘num‘. The ‘+‘ operator concatenates each number the user enters each time.

After getting all the numbers from the user, the numbers inside “numbers” list are sorted in ascending order using the sort() method and printed using the print() command.

using * operator

An empty list can be constructed using Python’s ‘*’ operator. The following code constructs an empty list with a length or size 3 using the multiplication operator ‘*' on an empty list []. Here is a breakdown of what the code does:

  1. Initializes an empty list empty_list.
  2. Multiplies the empty list [] by the integer 3.
  3. Assigns the resulting list to empty_list.
  4. Prints the value of empty_list, which is [].
  5. Prints the length of empty_list, which is 0.

In summary, this code creates an empty list with a length of 3 by multiplying an empty list by 3, but the resulting list is empty with a size/length of Zero.

# Creates an empty list with a length or size of 3
empty_list = [] * 3
print('empty_list: ', empty_list)
print("length of empty_list:", len(empty_list))
empty_list:  []
length of empty_list: 0

PRACTICAL useS FOR Empty ListS

In Python, an empty list serves as a placeholder for a list we want to create but haven’t added any items. However, the items will be added later. Here are some specific cases where an empty list might be helpful:

  1. Initializing a list: When you want to initialize a list but don’t know its values, you can create an empty list and add elements later.
  2. Iterating through a loop: Sometimes, you can iterate and add elements to a list. In this case, you can create an empty list before the loop and add elements inside it.
  3. Returning a list from a function: If you have a function that returns a list but don’t yet know what values it will contain, you can create an empty list at the beginning of the function and add elements.
  4. Placeholder for an optional argument: In some functions, you may have an optional argument that can be a list. In this case, you can set the argument’s default value to an empty list, which will be filled with elements if the argument is provided.
  5. Checking if a list is empty: In some cases, you may want to check if a list is empty or not. However, In this case, you can use an empty list as a placeholder and check if it has any elements using the len() function or a boolean expression.

In summary, an empty list serves as a useful placeholder when you want to add elements to it at a later stage.

Approaches to creating an empty list in Python

Using list comprehension

Creates an empty list of lists using list comprehension. The code can be summed up as follows:

  1. Initializes the variable n to the integer 3.
  2. Creates an empty list of lists using a list comprehension, which iterates n times and generates an empty list at each iteration.
  3. Assigns the resulting list to the variable empty_list.
  4. Prints the value of empty_list, which contains three empty lists.

In summary, this code creates an empty list of lists with a length of 3 using list comprehension to generate three empty lists. The resulting list is assigned to the variable empty_list.

n = 3
#create an empty list 
empty_list = [[] for k in range(n)]
print(empty_list)

[[], [], []]

Creating an empty list of dictionaries

Constructs an empty list of dictionaries using list comprehension. The code looks like:

  1. Creates an empty dictionary using the dict() constructor.
  2. Initializes a variable '_' to an underscore character, commonly used to indicate that the variable’s value is not used in the loop.
  3. Use a list comprehension to generate four empty dictionaries by iterating four times and generating an empty dictionary at each iteration.
  4. Assigns the resulting list to the variable empty_dict_list.
  5. Prints the value of empty_dict_list, which contains four empty dictionaries.

In summary, this code creates an empty list of dictionaries with a length of 4 by using a list comprehension to generate four empty dictionaries. Therefore, the resulting list is assigned to the variable empty_dict_list.

#construct an empty dictionary lists
empty_dict_list = [dict() for _ in range(4)]
print(empty_dict_list)

[{}, {}, {}, {}]

modifying the above code by appending new key-value pairs

Code appends new key-value pairs to three dictionaries in the empty_dict_list list. Here is a breakdown of what the code does:

  1. Accesses the first dictionary in the list using indexing and assigns the value ‘pw123‘ to the key ‘xyz‘.
  2. Accesses the second dictionary in the list using indexing and assigns the value ‘pw456’ to the key ‘abc‘.
  3. Accesses the fourth dictionary in the list using indexing and assigns the value ‘pw789‘ to the key ‘123‘.
  4. Prints the value of empty_dict_list, four dictionaries with the new key-value pairs.

This code appends new key-value pairs to dictionaries in a list using indexing and assignment statements. However, the resulting list is printed to show the updated dictionaries.

# append dictionary:
empty_dict_list[0]['xyz'] = 'pw123'
empty_dict_list[1]['abc'] = 'pw456'
empty_dict_list[3]['123'] = 'pw789'
print(empty_dict_list)

[{'xyz': 'pw123'}, {'abc': 'pw456'}, {}, {'123': 'pw789'}]

Modifying the empty list in Python

  • An empty list is created using empty brackets: empty_list = []
  • The append() function is used to add elements to the list: empty_list.append('location = New York City')
  • Multiple elements can be added to the list using multiple append() functions.
  • However, the len() function is used to determine the length or size of the list: len(empty_list)
  • Elements of a list can be overwritten by assigning a new value to the index: empty_list[1] = 'wind_speed'
  • Individual elements of the list can be accessed using their index: empty_list[0]
  • The type() function is used to determine the data type of the list: type(empty_list)

Overwriting the elements of an existing list in Python

Code demonstrates how to overwrite the elements of an existing list in Python:

  • An empty list is created and assigned to the variable empty_list using empty square brackets [].
  • The append() method appends three new elements to the list.
  • The values of the list, its data type, and its size are displayed using the print() function.
  • However, the values of the second and third elements are overwritten with new values “wind_speed” and 10, respectively.
  • The value of the first element “location = New York City” is also overwritten with a new value “New York City“.
  • However, the final list is printed to display the updated values of its elements.
# creating empty list
empty_list = []
# append elements of the list 
empty_list.append('location = New York City')
empty_list.append('temperature = 30')
empty_list.append('humidity = 84')


print("Values of empty_list:", empty_list)
print("Type of empty_list:", type(empty_list))
print("Size of empty_list:", len(empty_list))
print('\n')

# Overwrite the elements
empty_list[1] = 'wind_speed'
empty_list[2] = 10
empty_list[0] = 'New York City'
print(empty_list)

Values of empty_list: ['location = New York City', 'temperature = 30', 'humidity = 84']
Type of empty_list: <class 'list'>
Size of empty_list: 3


['New York City', 'wind_speed', 10]

Conclusion

The article covers the basics of the create an empty list. Additionally, highlight when using an Empty List and various built-in functions to create an empty list in Python. Moreover, the functions used to do this particular task are using square brackets[], the list() function, list comprehension, and the * operator. Moreover, a construction list of empty dictionaries, appending lists, and dictionaries. However, all of these functions are explained with code examples in detail.

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