Python – Check If All Elements in List are Negative

In this tutorial, we will look at how to check if all the elements in a list are negative (less than 0) or not in Python with the help of some examples.

How to check if all the list items are negative?

You can use the Python built-in all() function to check if all the elements in a list are negative or not by comparing each value in the list with 0.

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 negative or not, use the all() function to check if all the values are less than 0. The following is the syntax –

# check if all the list values are negative
all(val < 0 for val in ls)

It returns True if all the values in the list are less than 0.

Note that there are other methods as well that you can use to check if all list values are negative or not. For example –

• Iterate through the list and keep a count of values that are less than 0. If this count is the same as the length of the list, you can say that all values are negative.

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 negative values
ls1 = [-1, -2, -3, -4, -5, -5]
# list with positive, negative and zero values
ls2 = [0, 1, 2, 3, -4, 5, -5]
# empty list
ls3 = []

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

Output:

[-1, -2, -3, -4, -5, -5]
[0, 1, 2, 3, -4, 5, -5]
[]

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

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

The idea here is to use the all() function to check if each list element is negative (less than 0).

You can use a list comprehension to create a list of boolean values – whether a list element is less than 0 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 negative
print(all([val < 0 for val in ls1]))
print(all([val < 0 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 < 0 for val in ls3])

Output:

True

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

# check if all list values are negative
print(all(val < 0 for val in ls1))
print(all(val < 0 for val in ls2))
print(all(val < 0 for val in ls3))

Output:

True
False
True

We get the same results as above.

Example 2 – Check if all list elements are negative using a for loop

The idea, here, is to iterate through the list and keep a count of negative values in the list. If the resulting count is the same as the length of the list, we can say that all the values in the list are negative.

def all_list_elements_negative(ls):
    count = 0
    for val in ls:
        if val < 0:
            count += 1
    return count == len(ls)

# check if all list values are negative
print(all_list_elements_negative(ls1))
print(all_list_elements_negative(ls2))
print(all_list_elements_negative(ls3))

Output:

True
False
True

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

Summary

In this tutorial, we looked at some different methods to check if all the values in a list are negative or not. The following are the different methods covered –

• Use the Python built-in all() function to check if each list element is less than zero.
• Iterate through the list elements and track the count of values that are less than zero and then compare this count with the length of the list.

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• Python – Check If All Elements in List are Positive
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• Python – Check If All Elements in List are Zero
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