def single_or_default_(
predicate: Optional[Predicate[_T]] = None, default_value: _T = None
) -> Callable[[Observable[_T]], Observable[_T]]:
"""Returns the only element of an observable sequence that matches
the predicate, or a default value if no such element exists this
method reports an exception if there is more than one element in the
observable sequence.
Examples:
>>> res = single_or_default()
>>> res = single_or_default(lambda x: x == 42)
>>> res = single_or_default(lambda x: x == 42, 0)
>>> res = single_or_default(None, 0)
Args:
predicate -- [Optional] A predicate function to evaluate for
elements in the source sequence.
default_value -- [Optional] The default value if the index is
outside the bounds of the source sequence.
Returns:
An observable Sequence containing the single 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.single_or_default(None, default_value)
)
else:
return single_or_default_async_(True, default_value)
def create():
def predicate(x):
if x < 4:
return False
else:
raise Exception(ex)
return xs.pipe(ops.single_or_default(predicate, 0))
def create():
def predicate(x):
return x % 2 == 1
return xs.pipe(ops.single_or_default(predicate, 0))
def create():
return xs.pipe(ops.single_or_default(None, 0))