# Source code for networkx.algorithms.assortativity.pairs

```"""Generators of  x-y pairs of node data."""
import networkx as nx

__all__ = ["node_attribute_xy", "node_degree_xy"]

[docs]
@nx._dispatchable(node_attrs="attribute")
def node_attribute_xy(G, attribute, nodes=None):
"""Returns iterator of node-attribute pairs for all edges in G.

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

attribute: key
The node attribute key.

nodes: list or iterable (optional)
Use only edges that are incident to specified nodes.
The default is all nodes.

Returns
-------
(x, y): 2-tuple
Generates 2-tuple of (attribute, attribute) values.

Examples
--------
>>> G = nx.DiGraph()
>>> G.add_node(1, color="red")
>>> G.add_node(2, color="blue")
>>> G.add_edge(1, 2)
>>> list(nx.node_attribute_xy(G, "color"))
[('red', 'blue')]

Notes
-----
For undirected graphs each edge is produced twice, once for each edge
representation (u, v) and (v, u), with the exception of self-loop edges
which only appear once.
"""
if nodes is None:
nodes = set(G)
else:
nodes = set(nodes)
Gnodes = G.nodes
for u, nbrsdict in G.adjacency():
if u not in nodes:
continue
uattr = Gnodes[u].get(attribute, None)
if G.is_multigraph():
for v, keys in nbrsdict.items():
vattr = Gnodes[v].get(attribute, None)
for _ in keys:
yield (uattr, vattr)
else:
for v in nbrsdict:
vattr = Gnodes[v].get(attribute, None)
yield (uattr, vattr)

[docs]
@nx._dispatchable(edge_attrs="weight")
def node_degree_xy(G, x="out", y="in", weight=None, nodes=None):
"""Generate node degree-degree pairs for edges in G.

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

x: string ('in','out')
The degree type for source node (directed graphs only).

y: string ('in','out')
The degree type for target node (directed graphs only).

weight: string or None, optional (default=None)
The edge attribute that holds the numerical value used
as a weight.  If None, then each edge has weight 1.
The degree is the sum of the edge weights adjacent to the node.

nodes: list or iterable (optional)
Use only edges that are adjacency to specified nodes.
The default is all nodes.

Returns
-------
(x, y): 2-tuple
Generates 2-tuple of (degree, degree) values.

Examples
--------
>>> G = nx.DiGraph()
>>> G.add_edge(1, 2)
>>> list(nx.node_degree_xy(G, x="out", y="in"))
[(1, 1)]
>>> list(nx.node_degree_xy(G, x="in", y="out"))
[(0, 0)]

Notes
-----
For undirected graphs each edge is produced twice, once for each edge
representation (u, v) and (v, u), with the exception of self-loop edges
which only appear once.
"""
nodes = set(G) if nodes is None else set(nodes)
if G.is_directed():
direction = {"out": G.out_degree, "in": G.in_degree}
xdeg = direction[x]
ydeg = direction[y]
else:
xdeg = ydeg = G.degree

for u, degu in xdeg(nodes, weight=weight):
# use G.edges to treat multigraphs correctly
neighbors = (nbr for _, nbr in G.edges(u) if nbr in nodes)
for _, degv in ydeg(neighbors, weight=weight):
yield degu, degv

```