def first_or_default_(
predicate: Optional[Predicate[_T]] = None,
default_value: Optional[_T] = None
) -> Callable[[Observable[_T]], Observable[_T]]:
"""Returns the first element of an observable sequence that
satisfies the condition in the predicate, or a default value if no
such element exists.
Examples:
>>> res = source.first_or_default()
>>> res = source.first_or_default(lambda x: x > 3)
>>> res = source.first_or_default(lambda x: x > 3, 0)
>>> res = source.first_or_default(None, 0)
Args:
source -- Observable sequence.
predicate -- [optional] A predicate function to evaluate for
elements in the source sequence.
default_value -- [Optional] The default value if no such element
exists. If not specified, defaults to None.
Returns:
A function that takes an observable source and reutrn an
observable sequence containing the first element in the
observable sequence that satisfies the condition in the
predicate, or a default value if no such element exists.
"""
if predicate:
return compose(ops.filter(predicate),
ops.first_or_default(None, default_value))
return first_or_default_async_(True, default_value)
def create():
def predicate(x):
if x < 4:
return False
else:
raise Exception(ex)
return xs.pipe(ops.first_or_default(predicate, 0))
def create():
def predicate(x):
return x % 2 == 1
return xs.pipe(ops.first_or_default(predicate, 0))
def create():
return xs.pipe(ops.first_or_default(None, 0))