Four ways to return a default value if None in Python

One of the most common tasks when working with variables in Python is to return a default value if a variable (or a dictionary item) is None or if it doesn’t even exist.

This quick guide explores four methods of returning a default value if a variable is None or doesn’t exist.

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How to return a default value if None

There are several ways to do to return a default value if a variable (or a dictionary item) is None or if it doesn’t exist:

1. Standard if statement
2. One-liner if/else statement
3. The get() method (only dictionaries)
4. The try/except statement

Let’s explore each approach with examples.

1. Standard if statement: The simplest and most readable way of returning a default value – if a variable is None – is to use a standard if block. 

Here’s how you’d do it:

def get_name():
    return None

name = get_name()

# Set a default value if the name is None
if name is None:
   name = 'User'

print(name)
# Output: User

In the above example, we have a function get_name(), which is supposed to return a value to the caller. The function's returned value is stored in the name variable. If the function returns None, we set the name to User.

This way, you won't need an else block.

2. One-liner if/else statement: The previous method could be rewritten in one line. This is probably the most Pythonic way of doing this, even though it's less intuitive than a simple if.

def get_name():
   return 'some value'

name = 'User' if get_name() is None else get_name()
print(name)
# Output: some value

The above example works as it reads: set the name to 'User' if get_name() returns None. Otherwise, use get_name() return value.

3. Using or: If you're sure the returned value is either a string or None, you can use the "value or 'default'" syntax:

def get_name():
    return None

name = get_name() or 'User'
print(name)
# Output: User

This syntax returns the lefthand side value if it's truthy. Otherwise, it'll return the value on the right.

Values that are equivalent to false (in if and while statements) in Python are:

• None
• 0
• False
• Any object that its __len__() method returns 0 (e.g., dictionaries, lists, tuples, empty strings, etc.)

Tip: You can also use this technique to return a default value for empty strings.

While this works well, you should be aware the above example still returns 'User' if get_name() returns one of the above "falsy" values. However, if you know the value is either a string or None, it's an option you might want to consider.

3. The get() method (only dictionaries): You can use the get() method of a dict object and return a default value if a specific key doesn't exist.

Let's see an example:

person = {
    'first_name': 'John',
    'last_name': 'Smith',
    'department': None
}

print(person.get('age', 'Not specified'))
# Output: Not specified

print(person.get('department', 'Not specified'))
# Output: None

As you can see, if the key exists but it's None, it'll be returned. However, it might not be what you want.

To return a default value if the respective key is None, you can do so:

person = {
    'first_name': 'John',
    'last_name': 'Smith',
    'department': None
}

if 'department' not in person or person['department'] is None:
    person['department'] = 'default value'

print(person['department'])
# Output: default value

You can also use a try/except statement like so:

person = {
    'first_name': 'John',
    'last_name': 'Smith',
}

try: person['department']
except KeyError: person['department'] = 'default value'

print(person['department'])
# Output: default value

Or do it in two steps:

person = {
    'first_name': 'John',
    'last_name': 'Smith',
}

try: person['department']
except KeyError: person['department'] = None

if (person['department'] is None):
    person['department'] = 'default value'

print(person['department'])
# Output: default value

4. The try/except statement: As mentioned earlier, you can use the try/except statement to return a default value if a dictionary item is None. This technique isn't limited to dictionaries, though. 

You can use them for variables too. However, you must catch the NameError exception this time.

try: name
except NameError: name = None

if name is None:
    name = 'default value'

print(name)
# output: default value

The above snippet might seem redundant for many use cases. However, since Python doesn't have a function like isset() in PHP, this is how you can make it up.

Alright, I think it does it! I hope you found this quick guide helpful.

Thanks for reading!

Reza Lavarian Hey 👋 I'm a software engineer, an author, and an open-source contributor. I enjoy helping people (including myself) decode the complex side of technology. I share my findings on Twitter: @rezalavarian