Skip to main content



Parameters in the (which are accessible via the Flask app.config dictionary) are assumed to always be defined and thus should be accessed directly via,

blueprints = app.config["BLUEPRINTS"]

rather than,

blueprints = app.config.get("BLUEPRINTS")

or similar as the later will cause typing issues. The former is of type List[Callable] whereas the later is of type Optional[List[Callable]].



To ensure clarity, consistency, all readability, all new functions should use type hints and include a docstring.

Note per PEP-484 no syntax for listing explicitly raised exceptions is proposed and thus the recommendation is to put this information in a docstring, i.e.,

import math
from typing import Union

def sqrt(x: Union[float, int]) -> Union[float, int]:
Return the square root of x.

:param x: A number
:returns: The square root of the given number
:raises ValueError: If the number is negative

return math.sqrt(x)


TypeScript is fully supported and is the recommended language for writing all new frontend components. When modifying existing functions/components, migrating to TypeScript is appreciated, but not required. Examples of migrating functions/components to TypeScript can be found in #9162 and #9180.