Type annotation

Indicates that a variable, parameter, or return value can be absent (None) while otherwise holding a float.

Function parameters that may accept None, return values that may be missing, configuration values that are optional.

Python codebases using the typing module, data validation, API endpoints, configuration parsing.

Optional[; ]

Optional[; ]

inner_type: a type annotation such as float, int, str, or another Optional

• used in function signatures
• variable annotations
• return type hints
• dataclass fields
• Pydantic models.

• Optional[int]
• Optional[str]
• Optional[List[float]]
• Union[float
• None] (equivalent).

Confusing Optional[float] with float | None (though equivalent in Python 3.10+), forgetting to import Optional from typing, using Optional when a default value of None is not allowed.

Required float (just float) vs Optional[float]; Union[float, None] (explicit union); NonOptional containers like List[float] vs Optional[List[float]].

Coming from languages with nullable types (e.g., Kotlin's Float?): may assume similar null safety; in Python, Optional is just a hint and does not enforce at runtime.

• Optional[type]
• Union[type
• None]
• type | None (Python 3.10+)

Optional[float] does not prevent assigning None at runtime; static checkers treat it as optional; at runtime it's just a float or None; performance impact negligible.

Makes intent explicit about missing values, helps static analysis catch bugs.

Think of a nullable float: 'maybe a number, maybe nothing'.

Using Protocol or TypedDict for more complex optional structures, or using NewType for domain-specific optional floats.