Declare a variable that can hold an integer or None, indicating optionality.

Signal to readers and type checkers that the variable is optional and initially unset.

When a variable may not have a value yet, e.g., before assignment or as a function parameter that may be omitted.

Function parameters, class attributes, local variables where an integer is optional.

x: Optional[T] = None

variable: Optional[type] = default

variable name, type, default value

• int
• str
• None

• x: int | None = None
• x: Optional[str] = None

forgetting to import Optional from typing, using bare None without type hint

x: int = 0 (non-optional), x: List[int] = None (list optional)

confusing Optional with plain None assignment without a type hint

• optional variable annotations

indicates that None is a legitimate, intended state for the variable, not just an uninitialized state

signals that the argument may be omitted or explicitly set to None, allowing flexible calls

Think of a variable that may hold a value or be empty.

Requires importing Optional from typing for Python versions <3.10; native union syntax available in 3.10+

x: int | None = None (using union type syntax introduced in Python 3.10)