To store and accumulate numeric scores keyed by string identifiers, such as evaluation metrics or scores.

Declare a variable for accumulating scores in algorithms, evaluations, or scoring systems.

When implementing scoring mechanisms, evaluation metrics, or any context where string-keyed numeric scores need to be accumulated.

Inside functions, methods, class attributes, or module-level globals where scoring is needed.

scores: Dict[str, float] = {}

variable_name: Type = default_value

scores: Dict[key_type, value_type] = {} where key_type=str, value_type=float

• .get
• .update
• .items
• .keys
• .values
• .pop

• scores: Dict[str
• int] = {}
• scores: Dict[str
• float] = dict()

Forgetting to import Dict from typing in Python <3.5; using mutable default argument in function parameters; mismatching key/value types.

Similar: counts: Dict[str, int] = {}; Contrasting: scores: List[float] = []

Confusing with list or set; forgetting to import typing.Dict in older Python versions.

• variable declaration
• type annotation
• dictionary initialization

The type annotation is advisory and not enforced at runtime without runtime checking tools.

Signals to readers that the variable will hold string-keyed float scores, guiding appropriate usage.

Think of a scoreboard mapping names to scores.

scores: DefaultDict[str, float] = defaultdict(float)