def first_(
predicate: Optional[Predicate[_T]] = None,
) -> Callable[[Observable[_T]], Observable[_T]]:
"""Returns the first element of an observable sequence that
satisfies the condition in the predicate if present else the first
item in the sequence.
Examples:
>>> res = res = first()(source)
>>> res = res = first(lambda x: x > 3)(source)
Args:
predicate -- [Optional] A predicate function to evaluate for
elements in the source sequence.
Returns:
A function that takes an observable source and returns an
observable sequence containing the first element in the
observable sequence that satisfies the condition in the predicate if
provided, else the first item in the sequence.
"""
if predicate:
return compose(ops.filter(predicate), ops.first())
return first_or_default_async_(False)
def test_first_async_one(self):
scheduler = TestScheduler()
xs = scheduler.create_hot_observable(on_next(150, 1), on_next(210, 2),
on_completed(250))
res = scheduler.start(lambda: xs.pipe(ops.first()))
assert res.messages == [on_next(210, 2), on_completed(210)]
assert xs.subscriptions == [subscribe(200, 210)]
def create():
def predicate(x):
if x < 4:
return False
else:
raise Exception(ex)
return xs.pipe(ops.first(predicate))
def test_first_async_error(self):
ex = "ex"
scheduler = TestScheduler()
xs = scheduler.create_hot_observable(on_next(150, 1),
on_error(210, ex))
res = scheduler.start(lambda: xs.pipe(ops.first()))
assert res.messages == [on_error(210, ex)]
assert xs.subscriptions == [subscribe(200, 210)]
def create():
return xs.pipe(ops.first(lambda x: x > 10))
def create():
return xs.pipe(ops.first(lambda x: x % 2 == 1))
def create():
return xs.pipe(ops.first())
def test_run_from_first(self):
result = reactivex.from_([1, 2, 3]).pipe(ops.first()).run()
assert result == 1
