When to use the return None statement in Python

The return statement in Python is used to end the execution of a function and return a specific value back to the caller.

This return value can then be used for further process by assigning it to a variable. When a function has no return statement or just the return keyword without any specific value, then it will return the default value None.

Consider the following examples:

def a():
    return "Hello"

def b():
    return

def c():
    return None

def d():
    x = 9

## Call the functions

print(a())  # Hello
print(b())  # None
print(c())  # None
print(d())  # None

The function a() in the example returns a specific string value ‘Hello’ back to the caller. Meanwhile, the function b() just specifies return without any specific value, so it returns None.

The c() function explicitly returns the value None, and the d() function doesn’t have a return statement, so it also returns None.

Since Python returns None by default, you might wonder, when do you need to return None explicitly in your code?

While there’s no difference between implicitly and explicitly returning a None value, there are times when you might want to provide the return None statement.

When you put the return None statement in your code, it’s clear that your function has completed its task without finding any meaningful value to return.

When you didn’t use the return None statement, the function call result becomes a bit ambiguous. There may be a bug in the function.

For example, suppose you have a function that finds a word from a list as follows:

def find_word(word_list, word):
    for w in word_list:
        if w == word:
            return w
    return None

coding_term = ["bug", "system", "shell"]

result = find_word(coding_term, "error")
print(result)  # None

Even if we don’t write the return None statement in the find_word() function, it will still return None when there’s no matching word in the list.

But defining the return None statement means we expect the function to do so. We explicitly tell anyone who reads the code that the function can and will return None if a certain condition is met.

Because a None is expected, you can also include code that handles this value in your program as follows:

result = find_word(coding_term, "error")

if result is None:
    print("The word is not found in the list!")

And that’s about it. You should explicitly write the return None statement only when there’s a possibility that your function might return nothing.

One example where the return None statement is not required is when a function is not expected to return anything, like the greet() function below:

def greet():
    print("Hello!")
    
result = greet()

print(result)  # None

The greet() function only prints a greeting to the terminal, so there’s no need to specify any return statement at all.

I hope this tutorial has helped you to understand when you need to use the return None statement explicitly. Happy coding! 👍