Denotes a nested list structure for storing matrices or tables of float values.

Indicates the expected data structure type for function parameters, return values, or variables in type hints.

When specifying type hints for functions that accept or return 2D float arrays, or when annotating variables representing matrices.

Function signatures, variable annotations, return type hints, data class fields, protocol definitions.

List[List[float]]

List[List[float]]

Outer List element type: inner List; inner List element type: float (can be substituted with other types like int, str).

• def
• :
• ->
• =
• matrix
• data
• rows
• columns

• List[List[int]]
• List[List[str]]
• Tuple[Tuple[float
• ...]
• ...]
• numpy.ndarray

Confusing with numpy.ndarray; forgetting to import List from typing; using bare list syntax without type arguments; assuming inner lists have equal length.

List[float] (1D list), Tuple[Tuple[float, ...], ...] (immutable matrix), numpy.ndarray, List[List[float | int]]

Confusing with NumPy's array shape and dtype; mixing row-major vs column-major assumptions.

• List[float]
• Dict[str
• int]
• Set[str]
• Tuple[float
• ...]

Represents a mutable, row-major matrix; inner lists may vary in length unless otherwise constrained.

Signals to readers and static type checkers that the data is a homogeneous 2D float matrix.

Think of a spreadsheet of numbers.

Use NumPy arrays for efficient matrix operations.