Python – Check if All Elements in List are True

In this tutorial, we will look at how to check if all the elements in a list are True or not in Python with the help of some examples.

How to check if all the list values are True?

You can use the Python built-in all() function to check if all the elements in a list are True or not.

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).

Now, if you want to check whether all the values in a list evaluate to True in a boolean context, directly pass the list as an argument to the all() function.

# check if all the list values are truthy
all(ls)

If, on the other hand, you want to check whether each value in the list is the boolean value True, then inside the all() function, use an iterator to check whether each list value is True or not.

# check if all the list values are True
all(val == True for val in ls)

It returns True if all the values in the list are True.

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 True values
ls1 = [True, True, True, True]
# list with not all values True
ls2 = [False, True, False, True]
# empty list
ls3 = []

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

Output:

[True, True, True, True]
[False, True, False, True]
[]

Here, we created three lists – ls1, ls2, and ls3. The list ls1 contains only True as its elements. The list ls2 has repeated values but not all values are True and the list ls3 is empty (it does not contain any elements).

Example 1 – Check if all the list elements are True using all()

As mentioned earlier, the all() function returns True if all the values in the iterable are truthy (evaluate to True in a boolean context).

Let’s now apply the all() function to the lists created above.

# check if all values in list evaluate to True
print(all(ls1))
print(all(ls2))
print(all(ls3))

Output:

True
False
True

We get True for ls1 and False for ls2. Note that if you apply the all() function to an empty list, you get True as the result.

Example 2 – Using all() on list with non-boolean values

Note that the all() does not exactly check for whether the individual values are True or False. Instead, it checks whether the individual values evaluate to True or False in a boolean context.

For example, the value 1 evaluates to True in a boolean context. Similarly, the values 0 and None, empty collections (such as lists), etc. evaluate to False in a boolean context. Non-empty collections, numeric values other than 0, etc. evaluate to True in a boolean context.

Let’s look at an example.

# list with truthy values
ls4 = [1, 3, 1, True]
print(all(ls4))

Output:

True

Here, we applied the all() function to a list containing truthy values (all the values result to True in a boolean context) and thus we get True as the output.

If, the above list has any falsy (evaluate to False in a boolean context) values, the all() function will result in False.

ls4 = [0, 3, 1, True]
print(all(ls4))

Output:

False

We get False as the result.

Now, depending on your use case, you might only want to check whether the values in a list are truthy or not. In that case, use the all() function directly and pass the list (or the iterable) as an argument.

If, on the other hand, you want to check whether all the values in a list are exactly equal to the boolean value True, then, inside the all() function, check if each value is exactly equal to True or not using an iterator.

Here’s an example.

# list with truthy values
ls4 = [1, 3, 1, True]
# check if all values are exactly True
print(all(val == True for val in ls4))

Output:

False

We get False as the output even if all the values in the above list are truthy.

Summary

In this tutorial, we looked at how to check if all the values in a list are True or not. The following are the key takeaways –

• Use the Python built-in all() function to check if all the elements in a list are truthy or not.
• In case you want to check whether each value is exactly True or not, iterate through each value and check if it’s equal to True using an iterator inside the all() function.

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