wip: Add is_ok() and is_err() typing.TypeGuard shorthands

[wbolster]

See #69

[wbolster]

blocked by

• TypeGuard functions not properly recognizing generic types python/mypy#11428

for the time being

[erencank]

blocked by

• TypeGuard functions not properly recognizing generic types python/mypy#11428

for the time being

Do you have any updates now that the issue was successfully closed, as I would want this to be implemented as well?

[wbolster]

this indeed works these days using

$ mypy --version
mypy 0.971 (compiled: yes)

the ci failure on

E   AttributeError: module 'flake8.options.config' has no attribute 'ConfigFileFinder'

is due to tholo/pytest-flake8#87

[wbolster]

i've updated and rebased and simplified this (draft) PR now that upstream mypy issues have been resolved

[wbolster]

E   AttributeError: module 'flake8.options.config' has no attribute 'ConfigFileFinder'

fixed via #101

[francium]

I'm using pyright and it's reporting these as Ok instead of Result. A simple fix is to define a identify function that makes the typechecker not report these as the literal types,

    def passthrough(o: Result[str, int]) -> Result[str, int]:
        return o

    o = passthrough(Ok('yay'))
    n = passthrough(Err(100))

Without this passthrough function, you don't get proper type checking in this case,

    """The module-level type guard shorthands work."""
    def passthrough(o: Result[str, int]) -> Result[str, int]:
        return o

    o = passthrough(Ok('yay'))
    n = passthrough(Err(100))

    # Type checkers supporting typing.TypeGuard should accept the code below:
    if not is_ok(o):
        _ = o.value + ""  # works only for str
              ^^^^^^^^^^^
              Operator "+" not supported for types "str | int" and "Literal['']" 
    if not is_err(n):
        _ = n.value + 0  # works only for int
              ^^^^^^^^^^^
              Operator "+" not supported for types "str | int" and "Literal[0]"

[francium]

Closing in favor of 135