Specifies that a variable, parameter, or return value should contain a list of integer elements for static type checking.

Communicates the expected element type of a list to type checkers and readers, enabling early detection of type mismatches.

Used when annotating function parameters, return values, or variables that are intended to hold lists of integers in code that uses type hints (PEP 484).

Found in function signatures, variable assignments, and return type annotations in Python codebases that employ type hints.

List[<type>]

List[element_type] where element_type is a type annotation.

• Used with variable names like data
• items
• numbers
• appears in signatures such as def process(items: List[int]) -> None:

• List[float] for a list of floats
• List[str] for strings
• List[Any] for heterogeneous lists.

Forgetting to import List from typing (or using built-in list in Python 3.9+), causing a NameError. Using the built-in list[int] syntax in Python versions prior to 3.9, resulting in a SyntaxError. Confusing List[int] with Tuple[int, ...], leading to type checker errors when a tuple is expected. Applying List[int] to a variable that may contain None; should use Optional[List[int]] or List[Optional[int]] as appropriate. Misspelling List as list (lowercase), which refers to the built‑in type and causes a NameError when used as a generic.

Tuple[int, ...] – a homogeneous tuple of integers versus a list which is variable‑length. Set[int] – an unordered collection of unique integers. list (built‑in) – the runtime type, not the typing generic.

Coming from Java: may expect List<int> syntax with angle brackets; in Python generics use square brackets and commas. Coming from C++: may confuse std::vector<int> with List[int]; note that Python lists are dynamic arrays and type hints are erased at runtime.

• List type annotations
• Dict type annotations
• Set type annotations
• Tuple type annotations

1) Do not use List[int] when the list may contain None or non‑int types; use Union or Optional instead.\n2) Type hints are erased at runtime, so they add no runtime overhead.\n3) An empty list [] satisfies List[int]; also note that bool is a subclass of int, so [True, False] passes List[int] checks, which can be surprising.

Enables static type checkers to catch mismatched element types early, improving code reliability and readability.

Think of a grocery list where every item must be an apple; List[int] says every element in the list must be an integer.

In Python 3.9+ the built‑in list type can be used as a generic: list[int] offers equivalent functionality with cleaner syntax.

Use the built‑in list[int] syntax available in Python 3.9+ for a more concise type hint.