single_or_default

single_or_default(predicate=None)

Returns the only element in an Enumerable collection that satisfies a given predicate. If no elements satisfy the predicate, then returns None.

If a predicate is given, then it must be the only element in the collection that satisfies the condition. If the collection contains no elements that satisfy the given predicate then None is returned. If the collections contains 2 or more matching elements then a MoreThanOneMatchingElementError is raised.

This is an executing function.

Parameters

predicate : condition to satisfy as a lambda function. Optional.

Returns

The only element in the Enumerable collection that matches the given predicate.

Example

from py_linq import Enumerable

Enumerable([
    {'value': 1},
    {'value': 2},
    {'value': 3}
]).single_or_default(lambda x: x['value'] == 1)
# {'value': 1}

Enumerable([
    {'value': 1},
    {'value': 2},
    {'value': 3}
]).single_or_default()
# MoreThanOneMatchingElementError

Enumerable([]).single_or_default()
# None