Optional and Union

Learn optional types with Optional and Union.

Optional and Union

Sometimes a value is either a specific type or None. Optional declares that: Optional[int] means either int or None.

When one of two different types is needed, use Union: Union[int, str] accepts either an integer or a string.

from typing import Optional, Union

def find(id: int) -> Optional[str]:
    if id == 1:
        return "Ayşe"
    return None

def parse(value: Union[int, str]) -> int:
    return int(value)

Python 3.10+ also allows the short int | str and int | None syntax; this lesson uses the typing module.

None safety and defaults

Before using a value from a function returning Optional[int], you should check for None. Otherwise calls like None.upper() raise an error.

Example: name = find(2) may return None. Guard with if name is not None:; otherwise use a default string.

With Union you list several types; the order does not matter, but pick a logical one for readability.

Exercise Optional-returning find function

Write find(id: int) -> Optional[str]. If id == 1 return "Ayşe"; otherwise return None. Import Optional from typing. Call print(find(1)) and print(find(2)).

Show example solution

from typing import Optional

def find(id: int) -> Optional[str]:
    if id == 1:
        return "Ayşe"
    return None

print(find(1))
print(find(2))

Test yourself

Import Optional

from typing import ____

def find(id: int) -> Optional[str]:
    return None

Show answer

from typing import Optional

def find(id: int) -> Optional[str]:
    return None

Match the Optional and Union uses

Optional[int]

int or None
Union[int, str]

int or str
int | str

Short syntax (3.10+)
if v is not None

None check
Which value is VALID for Optional[str]?
- Only a string
- Only None
- Any type
- String or None
Show answer

String or None — Optional[str] accepts str or None; both are valid.

Next lesson: typing.List and Dict

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