# Source code for networkx.algorithms.isolate

```"""
Functions for identifying isolate (degree zero) nodes.
"""

__all__ = ["is_isolate", "isolates", "number_of_isolates"]

[docs]def is_isolate(G, n):
"""Determines whether a node is an isolate.

An *isolate* is a node with no neighbors (that is, with degree
zero). For directed graphs, this means no in-neighbors and no
out-neighbors.

Parameters
----------
G : NetworkX graph

n : node
A node in `G`.

Returns
-------
is_isolate : bool
True if and only if `n` has no neighbors.

Examples
--------
>>> G = nx.Graph()
>>> G.add_edge(1, 2)
>>> G.add_node(3)
>>> nx.is_isolate(G, 2)
False
>>> nx.is_isolate(G, 3)
True
"""
return G.degree(n) == 0

[docs]def isolates(G):
"""Iterator over isolates in the graph.

An *isolate* is a node with no neighbors (that is, with degree
zero). For directed graphs, this means no in-neighbors and no
out-neighbors.

Parameters
----------
G : NetworkX graph

Returns
-------
iterator
An iterator over the isolates of `G`.

Examples
--------
To get a list of all isolates of a graph, use the :class:`list`
constructor::

>>> G = nx.Graph()
>>> G.add_edge(1, 2)
>>> G.add_node(3)
>>> list(nx.isolates(G))


To remove all isolates in the graph, first create a list of the
isolates, then use :meth:`Graph.remove_nodes_from`::

>>> G.remove_nodes_from(list(nx.isolates(G)))
>>> list(G)
[1, 2]

For digraphs, isolates have zero in-degree and zero out_degre::

>>> G = nx.DiGraph([(0, 1), (1, 2)])
>>> G.add_node(3)
>>> list(nx.isolates(G))


"""
return (n for n, d in G.degree() if d == 0)

[docs]def number_of_isolates(G):
"""Returns the number of isolates in the graph.

An *isolate* is a node with no neighbors (that is, with degree
zero). For directed graphs, this means no in-neighbors and no
out-neighbors.

Parameters
----------
G : NetworkX graph

Returns
-------
int
The number of degree zero nodes in the graph `G`.

"""
# TODO This can be parallelized.
return sum(1 for v in isolates(G))
```