[Python]How to Check if a List is Empty, and How to Create a Empty List

This article shows how to check if a list is empty, and how to create a empty list.

How to check if a list is empty

I show how to check if a list is empty.

The following three ways are explained below.

• Using "if not statement"
• Using "len( ) function"
• Comparison with empty list

Using "if not statement"

I show how to check if a list is empty by using "if not statement".

Converting an empty list to the boolean type returns False.

list_fruits = ["Apple", "Banana", "Orange"]
list_empty = []

print(bool(list_fruits))
# True

print(bool(list_empty))
# False

Use the above to check if a list is empty.

list_fruits = ["Apple", "Banana", "Orange"]
list_empty = []

if not list_fruits :
    print("list is empty")
else :
    print("list is not empty")
# list is not empty

if not list_empty :
    print("list is empty")
else :
    print("list is not empty")
# list is empty

This way is recommended in "PEP 8 -- Style Guide for Python Code".

・For sequences, (strings, lists, tuples), use the fact that empty sequences are false:

# Correct:
if not seq:
if seq:

# Wrong:
if len(seq):
if not len(seq):

Reference : PEP 8 – Style Guide for Python Code

Using "len( ) function"

I show how to check if a list is empty by using "len( ) function".

This is an example code.

list_fruits = ["Apple", "Banana", "Orange"]
list_empty = []

if len(list_fruits) == 0:
    print("list is empty")
else :
    print("list is not empty")
# list is not empty

if len(list_empty) == 0:
    print("list is empty")
else :
    print("list is not empty")
# list is empty

Comparison with empty list

I show how to check if a list is empty by using "len( ) function".

This is an example code.

list_fruits = ["Apple", "Banana", "Orange"]
list_empty = []

if list_fruits == []:
    print("list is empty")
else :
    print("list is not empty")
# list is not empty

if list_empty == []:
    print("list is empty")
else :
    print("list is not empty")
# list is empty

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How to create a empty list

I show how to create a empty list.

Using square brackets "[ ]"

I show how to create a empty list by using square brackets "[ ]".

This is an example code.

list_empty = []

print(list_empty)
# []

print(len(list_empty))
# 0

Using "list( ) function"

I show how to create a empty list by using "list( ) function".

This is an example code.

list_empty = list()

print(list_empty)
# []

print(len(list_empty))
# 0

[Supplement]How to create a empty 2D list

As supplement, I show how to create a empty 2D list.

In following example code, an empty list is created by two different ways.

num = 5
empty_list1 = [[]] * num
empty_list2 = [[] for _ in range(num)]

print(empty_list1)
# [[], [], [], [], []]
print(empty_list2)
# [[], [], [], [], []]

Both are empty lists, but behave differently.

In following example code, an element is added to the empty list.

empty_list1[0].append(1)
empty_list2[0].append(1)

print(empty_list1)
# [[1], [1], [1], [1], [1]]
print(empty_list2)
# [[1], [], [], [], []]

This is due to the fact that the all empty lists generated by " [ [ ] ]* num " are objects with the same id.

print(id(empty_list1[0]))
# 2135914429192
print(id(empty_list1[1]))
# 2135914429192

print(id(empty_list2[0]))
# 2135913306504
print(id(empty_list2[1]))
# 2135898942984

When creating an empty 2D list, it is preferable that each list be independent.

Therefore, it is better to generate an empty 2D list by " [ [ ] for _ in range(num) ] ".

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