Advanced Python Types¶

Here are some additional ideas that might be useful when working with Python types.

Using `Union` or `Optional`¶

If your code for some reason can't use |, for example if it's not in a type annotation but in something like response_model=, instead of using the vertical bar (|) you can use Union from typing.

For example, you could declare that something could be a str or None:

from typing import Union


def say_hi(name: Union[str, None]):
        print(f"Hi {name}!")

typing also has a shortcut to declare that something could be None, with Optional.

Here's a tip from my very subjective point of view:

🚨 Avoid using Optional[SomeType]
Instead ✨ use Union[SomeType, None] ✨.

Both are equivalent and underneath they are the same, but I would recommend Union instead of Optional because the word "optional" would seem to imply that the value is optional, and it actually means "it can be None", even if it's not optional and is still required.

I think Union[SomeType, None] is more explicit about what it means.

It's just about the words and names. But those words can affect how you and your teammates think about the code.

As an example, let's take this function:

from typing import Optional


def say_hi(name: Optional[str]):
    print(f"Hey {name}!")

The parameter name is defined as Optional[str], but it is not optional, you cannot call the function without the parameter:

say_hi()  # Oh, no, this throws an error! 😱

The name parameter is still required (not optional) because it doesn't have a default value. Still, name accepts None as the value:

say_hi(name=None)  # This works, None is valid 🎉

The good news is, in most cases, you will be able to simply use | to define unions of types:

def say_hi(name: str | None):
    print(f"Hey {name}!")

So, normally you don't have to worry about names like Optional and Union. 😎

Advanced Python Types¶

Using Union or Optional¶

Using `Union` or `Optional`¶