Exhaustiveness checking with pytype #1076
Description
In mypy there is a technique to implement exhaustiveness checking using the NoReturn type. The short version is that you can create a 'magic' function like so:
def assert_never(value: NoReturn) -> NoReturn:
assert False, f'Unhandled value: {value} ({type(value).__name__})'
and then call the magic function in an if block, e.g.:
from typing import Union
def get_float(num: Union[str, float]) -> float:
if isinstance(num, str):
return float(num)
else:
assert_never(num)
will throw a compile time error because it does not check the float type, while
def get_float(num: Union[str, float]) -> float:
if isinstance(num, str):
return float(num)
elif isinstance(num, float):
return num
else:
assert_never(num)
will not.
Does pytype support an equivalent?
See also: python/mypy#5818