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Type Hint

#python #programming #doc #typing #datamodel

  • Types are defined by supported operations
  • It is a documentation which can be checked by type checkers like MyPy
  • There is no impact on the execution of the code
  • How is: var_name: some_type (PEP 484)
  • It is not possible to make hints ever on the code, sometimes is quite impossible
  • PEP 484
  • [[yyih-duck-typing-vs-nominal-typing]]#
  • Some options that can be important for mypy tools
    • disallow-untyped-defs: not allow any function without type hint
    • disallow-incomplete-defs: not allow any function with incomplete type hint
  • mypy can have global configuration or have mypy.ini for each module
  • Give no space between : and variable and one space between the : and type
  • = space on both sides
  • You can use default value None with two syntax and Optional
    • def show_count(count: int, singular: str, plural: Optional[str] = None)
    • def show_count(count: int, singular: str, plural: str | None = None)
  • Any is a magic type which allow any operations and subclasses, therefore accept anything
  • Simply type annotation: str, float, int, bytes or classes
  • Union[A, B, Union[C, D, E]] = Union[A, B, C, D, E]
  • Generic Collections example:
  • NoReturn usually used for function that raises exception
def tokenize(text: str) -> list[str]:
    return text.upper().split()
  • Code above return a list of string
  • [[o4v3-typing-tuple]]#
  • [[0c3b-typing-maps]]#
  • Sequence or Iterable for parameters and list for return type
  • [[80tb-typing-callable]]#
  • [[m30e-parameterized-generics-and-typevar]]#
  • [[zon5-annotating-positional-only-and-variadic-parameters]]#

Warning

Avoid Optional and Union on return types, because the user need to test which type of variable was returned by the function

[!tip] Collection Type Parameters Use one of them int, float, complex
Use Union[float, Decimal, Fraction]
Use Iterable instead of Sequence
Use Iterator for return type on generator

from collections.abc import Iterable
FromTo = tuple[str, str]
def zip_replace(text: str, changes: Iterable[FromTo]) -> str:
    for from_, to in changes:
        text = text.replace(from_, to)
    return text

References

  • Ramalho, 2022, p172-179
  • Ramalho, 2022, p253-260
  • Ramalho, 2022, p260-265
  • Ramalho, 2022, p294