def get_fact_result(self) -> Result[str, Exception]:
"""Return a Result for a cat fact."""
return (
Result.of(
requests.get,
"https://cat-fact.herokuapp.com/facts/random",
# this is the default, but sometimes the type checker wants us
# to make it explicit. See python/mypy#3737 for deets.
catch=Exception,
)
.and_then(lambda resp: Result.of(resp.json))
.map(
lambda parsed: t.cast(
str, parsed.get("text", "Unexpected cat fact format!")
)
)
)
def test_collect_short_circuits(self) -> None:
"""Ensure collect does not iterate after an err is reached."""
until_err: t.List[Result[int, str]] = [Ok(1), Ok(2), Err("no")]
def _iterable() -> t.Iterable[Result[int, str]]:
yield from until_err
# If we continue iterating after the err, we will raise a
# runtime Error.
assert False, "Result.collect() did not short circuit on err!"
assert Result.collect(_iterable()) == Err("no")
def get_fact(self) -> str:
"""Get a cat fact!"""
return (
# Create a Result from making our GET request.
# Now we can start chaining!
Result.of(
requests.get, "https://cat-fact.herokuapp.com/facts/random"
)
# Let's first consider the success path.
# If we got a response, it should be JSON, so let's try to parse
.and_then(lambda resp: Result.of(resp.json))
# If we successfully parsed JSON, we must have a dict, so let's
# grab our cat fact, or a useful message.
.map(
lambda parsed: t.cast(
str, parsed.get("text", "Unexpected cat fact format!")
)
)
# From here, all we need to do to consider the error case is
# convert our Err type (which for Result.of() is any exception
# that was raised) into the expected return type, which we
# do by passing the error to `str()`
.unwrap_or_else(str)
)
def test_result_cannot_be_instantiated(self) -> None:
"""Result cannot be instantiated"""
with pytest.raises(NotImplementedError):
r: Result[str, str] = Result("a")
assert r
def test_ok_if(self, predicate: t.Callable, val: t.Any,
exp: Result) -> None:
"""Test constructing based on some predicate."""
assert Result.ok_if(predicate, val) == exp
def test_collect(self, iterable: t.Iterable[Result[int, str]],
exp: Result[int, str]) -> None:
"""Test collecting an iterable of results into a single result."""
assert Result.collect(iterable) == exp
def test_of_with_kwargs(self) -> None:
"""Test getting a result from a callable with args."""
def foo(a: int, b: str = None) -> t.Optional[str]:
return b
assert Result.of(foo, 1, b="a").unwrap() == "a"
def test_of_with_args(self) -> None:
"""Test getting a result from a callable with args."""
assert Result.of(lambda x: bool(x > 0), 1).unwrap() is True
def test_of(self, fn: t.Callable, exp: Result) -> None:
"""Test getting a result from a callable."""
if exp.is_err():
assert isinstance(Result.of(fn).unwrap_err(), exp.unwrap_err())
else:
assert Result.of(fn) == exp
