collections.iterator

Module nu.forms.collections.iterator_.

Iterator - lazy stream form.

Name	Sort	Call	Meaning
Iterator	`stream_query`	`Iterator()`	Lazy stream over another form's elements.

Iterator

Lazy stream over another form's elements.

Iterator()

Path nu.forms.Iterator. Kind StreamQuery, sort stream_query, cardinality stream.

Opened by .iter() on an IterableForm, which wraps the source in a stream-shaped Iter term. A term of this shape produces its items one at a time rather than as a single value, so it sits wherever a stream goes: nu.ForEachDo, nu.Map, nu.Collect, and the itertools.

Notes

Stream-shaped, not scalar. Its surface is stream operations only: map/filter stay streams, to_list/to_set/to_tuple drain it into a concrete collection, next pulls one item.
No == / !=: an iterator has no value to compare, so both raise. Drain it first: it.to_list() == [...].
An element type rides on the payload as type_info when the source declared one (a typed collection ref opened with .iter()). The item first reads takes that type's form, and every op whose items are still the source's (filter, to_list, to_set) carries it on. map does not: the transform makes new items.

Example

nu.run(nu.List.of(1, 2, 3).iter().to_list())[0]

[1, 2, 3]

Methods

`.first()`

The first item this stream yields.

Yields

The first item. EMPTY when the stream is empty.

Notes

The stream opens fresh on every evaluation, so there is no cursor to advance: this is its first item, pulled and nothing past it. Python's next() is blocked by the Nu base.
The item takes the declared element type's form when the stream carries one, Object otherwise.

Example

nu.run(nu.List.of(1, 2).iter().first())[0]

`.map(transform, key=None)`

Each item replaced by transform's value, still a stream.

Builds Iterator.

Arguments

Name	Type	Default	Meaning
`transform`	`Nu \| Callable[[Attr], Nu]`		evaluated once per item; its value replaces the item. A lambda over the item, or a tree reading it with `nu.Attr(key)`.
`key`	`StrArg \| None`	`None`	the name each item is bound under, for a tree transform. Defaults to `"item"`; a lambda mints its own.

Yields

An Iterator the same length as self, lazily mapped.

Notes

The same binding as nu.Map: key is passed on only when given, so a lambda and an explicit name never meet.

Examples

xs = nu.List.of(1, 2).iter()
nu.run(xs.map(lambda x: nu.Int(x) + 1).to_list())[0]

[2, 3]

The same with a tree reading the default name:

nu.run(xs.map(nu.Add(nu.Attr("item"), 1)).to_list())[0]

[2, 3]

`.filter(predicate, key=None)`

Only the items predicate holds for, still a stream.

Builds Iterator[T].

Arguments

Name	Type	Default	Meaning
`predicate`	`Nu \| Callable[[Attr], Nu]`		evaluated once per item; the item stays when it is truthy. A lambda over the item, or a tree reading it with `nu.Attr(key)`.
`key`	`StrArg \| None`	`None`	the name each item is bound under, for a tree predicate. Defaults to `"item"`; a lambda mints its own.

Yields

An Iterator over the kept items, in order.

Notes

The same binding as nu.Filter: key is passed on only when given, so a lambda and an explicit name never meet.

Examples

xs = nu.List.of(1, 2, 3).iter()
nu.run(xs.filter(lambda x: x > 1).to_list())[0]

[2, 3]

The same with a tree reading an explicit name:

nu.run(xs.filter(nu.Gt(nu.Attr("n"), 1), key="n").to_list())[0]

[2, 3]

`.to_list()`

Self drained into a List, in order.

Builds List[T].

Yields

The List of items pulled.

Example

nu.run(nu.List.of(1, 2).iter().to_list())[0]

[1, 2]

`.to_set()`

Self drained into a Set.

Builds Set[T].

Yields

The Set of items pulled.

Notes

Duplicate items collapse; order is not preserved.

Example

nu.run(nu.List.of(1, 1, 2).iter().to_set())[0]

{1, 2}

`.to_tuple()`

Self drained into a Tuple, in order.

Builds Tuple.

Yields

The Tuple of items pulled.

Example

nu.run(nu.List.of(1, 2).iter().to_tuple())[0]

(1, 2)

Inherited methods

From nu.lang.forms.Form:

Call	Builds	Meaning
`.is_empty()`	`Bool`	True if this Form yields the EMPTY sentinel.
`.not_empty()`	`Bool`	True if this Form does not yield EMPTY.
`.fallback(*alternatives)`	`Self`	The first of this value and `alternatives` that is not EMPTY.

collections.iterator_

Iterator

.first()

.map(transform, key=None)

.filter(predicate, key=None)

.to_list()

.to_set()

.to_tuple()

On this page

`.first()`

`.map(transform, key=None)`

`.filter(predicate, key=None)`

`.to_list()`

`.to_set()`

`.to_tuple()`