Check If a List Contains Only Numbers in Python

In this tutorial, we will look at how to check if a list contains only numbers in Python with the help of some examples.

How to check if all list elements are numbers?

Check if list contains only numbers in python

You can use a combination of the Python built-in isinstance() and all() function to check if a list contains only numbers. For instance, you can use the following steps to check if all elements in a list are integers in Python –

In a list comprehension, for each element in the list, check if it’s an integer using the isinstance() function.
Apply the Python built-in all() function to return True only if all the items in the above list comprehension correspond to True.

The following is the code to check if all elements in a list are integers or not.

# check if all elements in ls are integers
all([isinstance(item, int) for item in ls])

Let’s take a look at an example.

# list of numbers
ls = [1, 2, 3, 4]
# check if list contains only numbers
print(all([isinstance(item, int) for item in ls]))

Output:

True

We get True as the output as all elements in the list ls are integers.

Let’s take a look at another example.

# list of numbers and a string
ls = [1, 2, 3, 4, 'cat']
# check if list contains only numbers
print(all([isinstance(item, int) for item in ls]))

Output:

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False

Here we get False as the output because not all elements in the list ls are integers. One element, “cat” in the list is a string.

Check if all items in a list of strings are numeric

If you, however, have a list of strings and want to check whether all the elements in the list are digits or not, you can use the following code.

# list of numeric strings
ls = ["1", "2", "3", "4"]
# check if list of string contains only numberic elements
print(all([item.isdigit() for item in ls]))

Output:

True

Here we check whether each element in the list of strings, ls is a numerical value or not using the string isdigit() function. We get True as the output as all the strings in the list ls are numeric characters.

Author

Piyush Raj

Piyush is a data professional passionate about using data to understand things better and make informed decisions. He has experience working as a Data Scientist in the consulting domain and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.

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