Python – Check If All Elements in List are None

In this tutorial, we will look at how to check if all the elements in a list are None (equal to the value None) or not in Python with the help of some examples.

How to check if all the list items are None?

You can use the Python built-in all() function to check if all the elements in a list are None or not by comparing each value in the list with None.

The all() function takes in an iterable as an argument and returns True if all the values in the iterable are truthy (represent True in a boolean context).

So, to check if all the values in a given list are zero or not, use the all() function to check if all the values are equal None. The following is the syntax –

# check if all the list values are None
all(val == None for val in ls)

It returns True if all the values in the list are equal to None.

Note that there are other methods as well that you can use to check if all list values are None or not. Some of them are –

• Iterate through the list and keep a count of values that are None. If this count is the same as the length of the list, you can say that all values are None.
• Create a set from list values and check if the set is equal to {None}.

Examples

Let’s now look at some examples of using the above methods. First, we will create a few lists that we’ll use to demonstrate the methods.

# list with all values as zero
ls1 = [None, None, None, None]
# list with different values
ls2 = [0, 1, 2, None, 4, 5, 5]
# empty list
ls3 = []

# display the lists
print(ls1)
print(ls2)
print(ls3)

Output:

[None, None, None, None]
[0, 1, 2, None, 4, 5, 5]
[]

Here, we created three lists – ls1, ls2, and ls3. The list ls1 contains only the value None as its elements. The list ls2 has repeated values but not all values are equal to None and the list ls3 is empty (it does not contain any elements).

Example 1 – Check if all the list elements are None using all()

The idea here is to use the all() function to check if each list element is equal to None.

You can use a list comprehension to create a list of boolean values – whether a list element is equal to None or not and then pass this resulting list as an argument to the all() function.

Let’s apply this to the lists ls1 and ls2 created above.

# check if all list values are None
print(all([val == None for val in ls1]))
print(all([val == None for val in ls2]))

Output:

True
False

We get True for ls1 and False for ls2.

If you apply this method to an empty list, you’ll get True as the output.

all([val == None for val in ls3])

Output:

True

Note that the all() function takes an iterable as an argument, so you can directly use an iterator (without using a list comprehension).

# check if all list values are None
print(all(val == None for val in ls1))
print(all(val == None for val in ls2))
print(all(val == None for val in ls3))

Output:

True
False
True

We get the same results as above.

Example 2 – Check if all list elements are None using a for loop

The idea, here, is to iterate through the list and keep a count of values that are equal to None. If the resulting count is the same as the length of the list, we can say that all the values in the list are None.

def all_list_elements_none(ls):
    count = 0
    for val in ls:
        if val == None:
            count += 1
    return count == len(ls)

# check if all list values are none
print(all_list_elements_none(ls1))
print(all_list_elements_none(ls2))
print(all_list_elements_none(ls3))

Output:

True
False
True

We get True for ls1 and False for ls2. Note that here we get True for an empty list.

Example 3 – Check if all the list elements are None using a set

In this method, we create a set from the list elements and check if the resulting set is equal to the set {None}. If the list has only None as its elements, the resulting set will be {None} (that is, a set with only None as the value).

# check if all list values are zero
print(set(ls1) == {0})
print(set(ls2) == {0})
print(set(ls3) == {0})

Output:

True
False
False

We get True for ls1 and False for ls2 and ls3. Note that here we get False for an empty list.

Summary

In this tutorial, we looked at some different methods to check if all the values in a list are None or not. The following are the different methods covered –

• Use the Python built-in all() function to check if each list element is equal to None.
• Iterate through the list elements and track the count of values that are None and then compare this count with the length of the list.
• Convert the list to a set and check if the resulting set is {None}.

You might also be interested in –

• Python – Check If All Elements in List are Zero
• Python – Check If All List Elements are of the same Type
• Python – Check If All Elements in a List are Unique
• Check If a List Contains Only Numbers in Python
• Python – Check List Contains All Elements Of Another List
• Python – Check if an element is in a list
• Python – Check If List Is Sorted Or Not