[Tut] How to Create an Empty List in Python?

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How to Create an Empty List in Python?

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To create an empty list in Python, you can use two ways. First, the empty square bracket notation

Code:

[]

creates a new list object without any element in it. Second, the

Code:

list()

initializer method without an argument creates an empty list object too.

Both approaches are shown in the following code:

Code:

# Way 1 to create an empty list: my_list = [] # Way 2 to create an empty list: my_list = list()

Next, you’ll learn many more related Python concepts you need to know that concern creation of lists. Keep reading to keep improving your skills and answer any subsequent question you may have!

Python list() — Quick Guide



Python’s built-in

Code:

list()

function creates and returns a new list object. When used without an argument, it returns an empty list. When used with the optional

Code:

iterable

argument, it initializes the new list with the elements in the iterable.

You can create an empty list by skipping the argument:

Code:

>>> list() []

If you pass an iterable—such as another list, a tuple, a set, or a dictionary—you obtain a new list object with list elements obtained from the iterable:

Code:

>>> list([1, 2, 3]) [1, 2, 3]

Read More: Read our full tutorial on the Finxter blog to learn everything you need to know.

Python Create Empty List of Size

To create a list of

Code:

n

placeholder elements, multiply the list of a single placeholder element with

Code:

n

.

For example, use

Code:

[None] * 5

to create a list

Code:

[None, None, None, None, None]

with five elements

Code:

None

.

You can then overwrite some elements with index assignments.

In the example,

Code:

lst[2] = 42

would result in the changed list

Code:

[None, None, 42, None, None]

.

Code:

# Create a list with n placeholder elements n = 5 lst = [None] * n # Print the "placeholder" list: print(lst) # [None, None, None, None, None] # Overwrite the placeholder elements lst[0] = 'Alice' lst[1] = 0 lst[2] = 42 lst[3] = 12 lst[4] = 'hello' print(lst) # ['Alice', 0, 42, 12, 'hello']

Read More: Read our full tutorial on the Finxter blog to learn everything you need to know.

Python Create Empty List of Lists

You can create an empty list of lists do not use

Code:

[[]] * n

because this creates a nested list that contains the same empty list object n times which can cause problems because if you update one, all inner lists change!

To create an empty list of lists with n empty inner lists, use the list comprehension statement

Code:

[[] for _ in range(n)]

that creates a fresh empty list object

Code:

n

times.

Code:

n = 5 my_list = [[] for _ in range(n)] print(my_list) # [[], [], [], [], []]

List comprehension is a powerful Python feature and I’ve written a full blog tutorial on it—feel free to watch my general explainer video and read the associated blog article!



Read More: Read our full tutorial on the Finxter blog to learn everything you need to know.

Python Create Empty List and Append in Loop

Follow these three easy steps to create an empty list and append values to it in a

Code:

for

loop:

1. Code:

   my_list = []
   creates the empty list and assigns it to the name
   Code:

   my_list
   .
   
   
2. Code:

   for i in range(10):
   initializes the for loop to be repeated 10 times using loop variable
   Code:

   i
   that takes on all values between 0, 1, …, 9.
   
   
3. Code:

   my_list.append(i)
   is the loop body that appends the integer value of the loop variable
   Code:

   i
   to the list.
   

Here’s the code example:

Code:

my_list = [] for i in range(10): my_list.append(i) print(my_list) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

However, a better Python one-liner alternative is using list comprehension for this:

Code:

my_list = [i for i in range(10)]

Python Create List of Empty Strings

To create a list of

Code:

n

empty strings, you can use the expression

Code:

[''] * n

because it places the same empty string literal

Code:

''

into the list

Code:

n

times. This doesn’t cause any problems due to the fact that all list elements refer to the same empty string object because strings are immutable and cannot be modified anyways.

Code:

>>> [''] * 5 ['', '', '', '', ''] >>> [''] * 20 ['', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '']

Python Create Empty List of Dictionaries

To create a list of

Code:

n

dictionaries, each dict being empty, use the list comprehension statement

Code:

[dict() for _ in range(n)]

with the underscore

Code:

_

as a throw-away “loop variable” and the

Code:

dict()

built-in dictionary creation function.

Code:

my_list = [dict() for _ in range(10)] print(my_list) # [{}, {}, {}, {}, {}, {}, {}, {}, {}, {}]

Note that if you update one of the dictionaries, all other dictionaries are unaffected by this because we really created n independent dictionary objects.

Code:

# update first dictionary: my_list[0]['foo'] = 'bar' print(my_list) # [{'foo': 'bar'}, {}, {}, {}, {}, {}, {}, {}, {}, {}]

Python Create Empty List of Class Objects

To create an empty list of class objects, you can use list comprehension statement

Code:

my_list = [MyClass() for _ in range(n)]

that repeats

Code:

n

times the creation of an empty class object

Code:

MyClass

and adding it to the list. You can then later change the contents of the

Code:

n

different

Code:

MyClass

objects.

Code:

class MyClass(object): pass my_list = [MyClass() for _ in range(5)] print(my_list) # [<__main__.MyClass object at 0x000001EA45779F40>, <__main__.MyClass object at 0x000001EA47533D00>, <__main__.MyClass object at 0x000001EA475334C0>, <__main__.MyClass object at 0x000001EA4758E070>, <__main__.MyClass object at 0x000001EA4758E4F0>]

Python Create Empty List of Type

Python is a dynamic language so there is no concept of a “list of type X”. Instead of creating a list of a fixed type, simply create an empty list using

Code:

[]

or

Code:

list()

and assign it to a variable such as

Code:

my_list

. Using the variable, you can then fill into the existing list any data type you want!

Here we create an empty list and fill in an integer, a list, and a string—all into the same list!

Code:

my_list = [] # Alternative: my_list = list() # Add integer to list: my_list.append(42) # Add list to list: my_list.append([1, 2, 3]) # Add string to list: my_list.append('hello world') # Print all contents of list: print(my_list) # [42, [1, 2, 3], 'hello world']

Python Create Empty List of Integers

To initialize a list with certain integers such as zeroes 0, you can either use the concise list multiplication operation

Code:

[0] * n

or you use list comprehension

Code:

[0 for _ in range(n)]

.

Code:

>>> [0] * 5 [0, 0, 0, 0, 0] >>> [0] * 10 [0, 0, 0, 0, 0, 0, 0, 0, 0, 0] >>> [42] * 5 [42, 42, 42, 42, 42] >>> [42 for _ in range(5)] [42, 42, 42, 42, 42]

Python Create Empty List of Tuples

To create an empty list and later add one tuple at-a-time to it, first initialize the empty list using the

Code:

[]

square bracket operator and then use the

Code:

list.append(t)

to append one tuple

Code:

t

at a time.

Here we add three tuples to the initially empty list:

Code:

# create empty list: my_list = [] # append tuples my_list.append((1, 2)) my_list.append(('alice', 'bob', 'carl')) my_list.append(tuple()) print(my_list) # [(1, 2), ('alice', 'bob', 'carl'), ()]