Format w/ black

10 files changed, 160 insertions, 153 deletions

diff --git a/networkx/readwrite/json_graph/adjacency.py b/networkx/readwrite/json_graph/adjacency.py
index f4a42d2a..ec6d21a4 100644
--- a/networkx/readwrite/json_graph/adjacency.py
+++ b/networkx/readwrite/json_graph/adjacency.py
@@ -1,9 +1,9 @@
 from itertools import chain
 import networkx as nx
 
-__all__ = ['adjacency_data', 'adjacency_graph']
+__all__ = ["adjacency_data", "adjacency_graph"]
 
-_attrs = dict(id='id', key='key')
+_attrs = dict(id="id", key="key")
 
 
 def adjacency_data(G, attrs=_attrs):
@@ -57,19 +57,19 @@ def adjacency_data(G, attrs=_attrs):
     adjacency_graph, node_link_data, tree_data
     """
     multigraph = G.is_multigraph()
-    id_ = attrs['id']
+    id_ = attrs["id"]
     # Allow 'key' to be omitted from attrs if the graph is not a multigraph.
-    key = None if not multigraph else attrs['key']
+    key = None if not multigraph else attrs["key"]
     if id_ == key:
-        raise nx.NetworkXError('Attribute names are not unique.')
+        raise nx.NetworkXError("Attribute names are not unique.")
     data = {}
-    data['directed'] = G.is_directed()
-    data['multigraph'] = multigraph
-    data['graph'] = list(G.graph.items())
-    data['nodes'] = []
-    data['adjacency'] = []
+    data["directed"] = G.is_directed()
+    data["multigraph"] = multigraph
+    data["graph"] = list(G.graph.items())
+    data["nodes"] = []
+    data["adjacency"] = []
     for n, nbrdict in G.adjacency():
-        data['nodes'].append(dict(chain(G.nodes[n].items(), [(id_, n)])))
+        data["nodes"].append(dict(chain(G.nodes[n].items(), [(id_, n)])))
         adj = []
         if multigraph:
             for nbr, keys in nbrdict.items():
@@ -78,7 +78,7 @@ def adjacency_data(G, attrs=_attrs):
         else:
             for nbr, d in nbrdict.items():
                 adj.append(dict(chain(d.items(), [(id_, nbr)])))
-        data['adjacency'].append(adj)
+        data["adjacency"].append(adj)
     return data
 
 
@@ -122,26 +122,26 @@ def adjacency_graph(data, directed=False, multigraph=True, attrs=_attrs):
     --------
     adjacency_graph, node_link_data, tree_data
     """
-    multigraph = data.get('multigraph', multigraph)
-    directed = data.get('directed', directed)
+    multigraph = data.get("multigraph", multigraph)
+    directed = data.get("directed", directed)
     if multigraph:
         graph = nx.MultiGraph()
     else:
         graph = nx.Graph()
     if directed:
         graph = graph.to_directed()
-    id_ = attrs['id']
+    id_ = attrs["id"]
     # Allow 'key' to be omitted from attrs if the graph is not a multigraph.
-    key = None if not multigraph else attrs['key']
-    graph.graph = dict(data.get('graph', []))
+    key = None if not multigraph else attrs["key"]
+    graph.graph = dict(data.get("graph", []))
     mapping = []
-    for d in data['nodes']:
+    for d in data["nodes"]:
         node_data = d.copy()
         node = node_data.pop(id_)
         mapping.append(node)
         graph.add_node(node)
         graph.nodes[node].update(node_data)
-    for i, d in enumerate(data['adjacency']):
+    for i, d in enumerate(data["adjacency"]):
         source = mapping[i]
         for tdata in d:
             target_data = tdata.copy()
diff --git a/networkx/readwrite/json_graph/cytoscape.py b/networkx/readwrite/json_graph/cytoscape.py
index 202d6a03..1a6f0c06 100644
--- a/networkx/readwrite/json_graph/cytoscape.py
+++ b/networkx/readwrite/json_graph/cytoscape.py
@@ -1,8 +1,8 @@
 import networkx as nx
 
-__all__ = ['cytoscape_data', 'cytoscape_graph']
+__all__ = ["cytoscape_data", "cytoscape_graph"]
 
-_attrs = dict(name='name', ident='id')
+_attrs = dict(name="name", ident="id")
 
 
 def cytoscape_data(G, attrs=None):
@@ -31,11 +31,11 @@ def cytoscape_data(G, attrs=None):
     ident = attrs["ident"]
 
     if len({name, ident}) < 2:
-        raise nx.NetworkXError('Attribute names are not unique.')
+        raise nx.NetworkXError("Attribute names are not unique.")
 
     jsondata = {"data": list(G.graph.items())}
-    jsondata['directed'] = G.is_directed()
-    jsondata['multigraph'] = G.is_multigraph()
+    jsondata["directed"] = G.is_directed()
+    jsondata["multigraph"] = G.is_multigraph()
     jsondata["elements"] = {"nodes": [], "edges": []}
     nodes = jsondata["elements"]["nodes"]
     edges = jsondata["elements"]["edges"]
@@ -73,17 +73,17 @@ def cytoscape_graph(data, attrs=None):
     ident = attrs["ident"]
 
     if len({ident, name}) < 2:
-        raise nx.NetworkXError('Attribute names are not unique.')
+        raise nx.NetworkXError("Attribute names are not unique.")
 
-    multigraph = data.get('multigraph')
-    directed = data.get('directed')
+    multigraph = data.get("multigraph")
+    directed = data.get("directed")
     if multigraph:
         graph = nx.MultiGraph()
     else:
         graph = nx.Graph()
     if directed:
         graph = graph.to_directed()
-    graph.graph = dict(data.get('data'))
+    graph.graph = dict(data.get("data"))
     for d in data["elements"]["nodes"]:
         node_data = d["data"].copy()
         node = d["data"]["value"]
diff --git a/networkx/readwrite/json_graph/jit.py b/networkx/readwrite/json_graph/jit.py
index f404003c..ccef18b6 100644
--- a/networkx/readwrite/json_graph/jit.py
+++ b/networkx/readwrite/json_graph/jit.py
@@ -30,7 +30,7 @@ import json
 import networkx as nx
 from networkx.utils.decorators import not_implemented_for
 
-__all__ = ['jit_graph', 'jit_data']
+__all__ = ["jit_graph", "jit_data"]
 
 
 def jit_graph(data, create_using=None):
@@ -57,14 +57,14 @@ def jit_graph(data, create_using=None):
         data = json.loads(data)
 
     for node in data:
-        G.add_node(node['id'], **node['data'])
-        if node.get('adjacencies') is not None:
-            for adj in node['adjacencies']:
-                G.add_edge(node['id'], adj['nodeTo'], **adj['data'])
+        G.add_node(node["id"], **node["data"])
+        if node.get("adjacencies") is not None:
+            for adj in node["adjacencies"]:
+                G.add_edge(node["id"], adj["nodeTo"], **adj["data"])
     return G
 
 
-@not_implemented_for('multigraph')
+@not_implemented_for("multigraph")
 def jit_data(G, indent=None, default=None):
     """Returns data in JIT JSON format.
 
@@ -88,10 +88,7 @@ def jit_data(G, indent=None, default=None):
     """
     json_graph = []
     for node in G.nodes():
-        json_node = {
-            "id": node,
-            "name": node
-        }
+        json_node = {"id": node, "name": node}
         # node data
         json_node["data"] = G.nodes[node]
         # adjacencies
diff --git a/networkx/readwrite/json_graph/node_link.py b/networkx/readwrite/json_graph/node_link.py
index 721f0034..42c4d07f 100644
--- a/networkx/readwrite/json_graph/node_link.py
+++ b/networkx/readwrite/json_graph/node_link.py
@@ -1,11 +1,11 @@
 from itertools import chain, count
 import networkx as nx
 from networkx.utils import to_tuple
-__all__ = ['node_link_data', 'node_link_graph']
 
+__all__ = ["node_link_data", "node_link_graph"]
 
-_attrs = dict(source='source', target='target', name='id',
-              key='key', link='links')
+
+_attrs = dict(source="source", target="target", name="id", key="key", link="links")
 
 
 def node_link_data(G, attrs=None):
@@ -69,26 +69,30 @@ def node_link_data(G, attrs=None):
         attrs = _attrs
     else:
         attrs.update({k: v for (k, v) in _attrs.items() if k not in attrs})
-    name = attrs['name']
-    source = attrs['source']
-    target = attrs['target']
-    links = attrs['link']
+    name = attrs["name"]
+    source = attrs["source"]
+    target = attrs["target"]
+    links = attrs["link"]
     # Allow 'key' to be omitted from attrs if the graph is not a multigraph.
-    key = None if not multigraph else attrs['key']
+    key = None if not multigraph else attrs["key"]
     if len({source, target, key}) < 3:
-        raise nx.NetworkXError('Attribute names are not unique.')
-    data = {'directed': G.is_directed(), 'multigraph': multigraph, 'graph': G.graph,
-            'nodes': [dict(chain(G.nodes[n].items(), [(name, n)])) for n in G]}
+        raise nx.NetworkXError("Attribute names are not unique.")
+    data = {
+        "directed": G.is_directed(),
+        "multigraph": multigraph,
+        "graph": G.graph,
+        "nodes": [dict(chain(G.nodes[n].items(), [(name, n)])) for n in G],
+    }
     if multigraph:
         data[links] = [
-            dict(chain(d.items(),
-                       [(source, u), (target, v), (key, k)]))
-            for u, v, k, d in G.edges(keys=True, data=True)]
+            dict(chain(d.items(), [(source, u), (target, v), (key, k)]))
+            for u, v, k, d in G.edges(keys=True, data=True)
+        ]
     else:
         data[links] = [
-            dict(chain(d.items(),
-                       [(source, u), (target, v)]))
-            for u, v, d in G.edges(data=True)]
+            dict(chain(d.items(), [(source, u), (target, v)]))
+            for u, v, d in G.edges(data=True)
+        ]
     return data
 
 
@@ -139,23 +143,23 @@ def node_link_graph(data, directed=False, multigraph=True, attrs=None):
         attrs = _attrs
     else:
         attrs.update({k: v for k, v in _attrs.items() if k not in attrs})
-    multigraph = data.get('multigraph', multigraph)
-    directed = data.get('directed', directed)
+    multigraph = data.get("multigraph", multigraph)
+    directed = data.get("directed", directed)
     if multigraph:
         graph = nx.MultiGraph()
     else:
         graph = nx.Graph()
     if directed:
         graph = graph.to_directed()
-    name = attrs['name']
-    source = attrs['source']
-    target = attrs['target']
-    links = attrs['link']
+    name = attrs["name"]
+    source = attrs["source"]
+    target = attrs["target"]
+    links = attrs["link"]
     # Allow 'key' to be omitted from attrs if the graph is not a multigraph.
-    key = None if not multigraph else attrs['key']
-    graph.graph = data.get('graph', {})
+    key = None if not multigraph else attrs["key"]
+    graph.graph = data.get("graph", {})
     c = count()
-    for d in data['nodes']:
+    for d in data["nodes"]:
         node = to_tuple(d.get(name, next(c)))
         nodedata = {str(k): v for k, v in d.items() if k != name}
         graph.add_node(node, **nodedata)
@@ -163,12 +167,14 @@ def node_link_graph(data, directed=False, multigraph=True, attrs=None):
         src = tuple(d[source]) if isinstance(d[source], list) else d[source]
         tgt = tuple(d[target]) if isinstance(d[target], list) else d[target]
         if not multigraph:
-            edgedata = {str(k): v for k, v in d.items()
-                            if k != source and k != target}
+            edgedata = {str(k): v for k, v in d.items() if k != source and k != target}
             graph.add_edge(src, tgt, **edgedata)
         else:
             ky = d.get(key, None)
-            edgedata = {str(k): v for k, v in d.items()
-                            if k != source and k != target and k != key}
+            edgedata = {
+                str(k): v
+                for k, v in d.items()
+                if k != source and k != target and k != key
+            }
             graph.add_edge(src, tgt, ky, **edgedata)
     return graph
diff --git a/networkx/readwrite/json_graph/tests/test_adjacency.py b/networkx/readwrite/json_graph/tests/test_adjacency.py
index 08bbb5fe..57a2a6b1 100644
--- a/networkx/readwrite/json_graph/tests/test_adjacency.py
+++ b/networkx/readwrite/json_graph/tests/test_adjacency.py
@@ -5,7 +5,6 @@ from networkx.readwrite.json_graph import adjacency_data, adjacency_graph
 
 
 class TestAdjacency:
-
     def test_graph(self):
         G = nx.path_graph(4)
         H = adjacency_graph(adjacency_data(G))
@@ -13,22 +12,22 @@ class TestAdjacency:
 
     def test_graph_attributes(self):
         G = nx.path_graph(4)
-        G.add_node(1, color='red')
+        G.add_node(1, color="red")
         G.add_edge(1, 2, width=7)
-        G.graph['foo'] = 'bar'
-        G.graph[1] = 'one'
+        G.graph["foo"] = "bar"
+        G.graph[1] = "one"
 
         H = adjacency_graph(adjacency_data(G))
-        assert H.graph['foo'] == 'bar'
-        assert H.nodes[1]['color'] == 'red'
-        assert H[1][2]['width'] == 7
+        assert H.graph["foo"] == "bar"
+        assert H.nodes[1]["color"] == "red"
+        assert H[1][2]["width"] == 7
 
         d = json.dumps(adjacency_data(G))
         H = adjacency_graph(json.loads(d))
-        assert H.graph['foo'] == 'bar'
-        assert H.graph[1] == 'one'
-        assert H.nodes[1]['color'] == 'red'
-        assert H[1][2]['width'] == 7
+        assert H.graph["foo"] == "bar"
+        assert H.graph[1] == "one"
+        assert H.nodes[1]["color"] == "red"
+        assert H[1][2]["width"] == 7
 
     def test_digraph(self):
         G = nx.DiGraph()
@@ -46,14 +45,14 @@ class TestAdjacency:
 
     def test_multigraph(self):
         G = nx.MultiGraph()
-        G.add_edge(1, 2, key='first')
-        G.add_edge(1, 2, key='second', color='blue')
+        G.add_edge(1, 2, key="first")
+        G.add_edge(1, 2, key="second", color="blue")
         H = adjacency_graph(adjacency_data(G))
         nx.is_isomorphic(G, H)
-        assert H[1][2]['second']['color'] == 'blue'
+        assert H[1][2]["second"]["color"] == "blue"
 
     def test_exception(self):
         with pytest.raises(nx.NetworkXError):
             G = nx.MultiDiGraph()
-            attrs = dict(id='node', key='node')
+            attrs = dict(id="node", key="node")
             adjacency_data(G, attrs)
diff --git a/networkx/readwrite/json_graph/tests/test_cytoscape.py b/networkx/readwrite/json_graph/tests/test_cytoscape.py
index 16c917d9..ee4799fb 100644
--- a/networkx/readwrite/json_graph/tests/test_cytoscape.py
+++ b/networkx/readwrite/json_graph/tests/test_cytoscape.py
@@ -5,7 +5,6 @@ from networkx.readwrite.json_graph import cytoscape_data, cytoscape_graph
 
 
 class TestCytoscape:
-
     def test_graph(self):
         G = nx.path_graph(4)
         H = cytoscape_graph(cytoscape_data(G))
@@ -13,27 +12,27 @@ class TestCytoscape:
 
     def test_graph_attributes(self):
         G = nx.path_graph(4)
-        G.add_node(1, color='red')
+        G.add_node(1, color="red")
         G.add_edge(1, 2, width=7)
-        G.graph['foo'] = 'bar'
-        G.graph[1] = 'one'
+        G.graph["foo"] = "bar"
+        G.graph[1] = "one"
         G.add_node(3, name="node", id="123")
 
         H = cytoscape_graph(cytoscape_data(G))
-        assert H.graph['foo'] == 'bar'
-        assert H.nodes[1]['color'] == 'red'
-        assert H[1][2]['width'] == 7
-        assert H.nodes[3]['name'] == 'node'
-        assert H.nodes[3]['id'] == '123'
+        assert H.graph["foo"] == "bar"
+        assert H.nodes[1]["color"] == "red"
+        assert H[1][2]["width"] == 7
+        assert H.nodes[3]["name"] == "node"
+        assert H.nodes[3]["id"] == "123"
 
         d = json.dumps(cytoscape_data(G))
         H = cytoscape_graph(json.loads(d))
-        assert H.graph['foo'] == 'bar'
-        assert H.graph[1] == 'one'
-        assert H.nodes[1]['color'] == 'red'
-        assert H[1][2]['width'] == 7
-        assert H.nodes[3]['name'] == 'node'
-        assert H.nodes[3]['id'] == '123'
+        assert H.graph["foo"] == "bar"
+        assert H.graph[1] == "one"
+        assert H.nodes[1]["color"] == "red"
+        assert H[1][2]["width"] == 7
+        assert H.nodes[3]["name"] == "node"
+        assert H.nodes[3]["id"] == "123"
 
     def test_digraph(self):
         G = nx.DiGraph()
@@ -51,14 +50,14 @@ class TestCytoscape:
 
     def test_multigraph(self):
         G = nx.MultiGraph()
-        G.add_edge(1, 2, key='first')
-        G.add_edge(1, 2, key='second', color='blue')
+        G.add_edge(1, 2, key="first")
+        G.add_edge(1, 2, key="second", color="blue")
         H = cytoscape_graph(cytoscape_data(G))
         assert nx.is_isomorphic(G, H)
-        assert H[1][2]['second']['color'] == 'blue'
+        assert H[1][2]["second"]["color"] == "blue"
 
     def test_exception(self):
         with pytest.raises(nx.NetworkXError):
             G = nx.MultiDiGraph()
-            attrs = dict(name='node', ident='node')
+            attrs = dict(name="node", ident="node")
             cytoscape_data(G, attrs)
diff --git a/networkx/readwrite/json_graph/tests/test_jit.py b/networkx/readwrite/json_graph/tests/test_jit.py
index a251242f..9a2ef682 100644
--- a/networkx/readwrite/json_graph/tests/test_jit.py
+++ b/networkx/readwrite/json_graph/tests/test_jit.py
@@ -7,12 +7,12 @@ from networkx.readwrite.json_graph import jit_data, jit_graph
 class TestJIT:
     def test_jit(self):
         G = nx.Graph()
-        G.add_node('Node1', node_data='foobar')
-        G.add_node('Node3', node_data='bar')
-        G.add_node('Node4')
-        G.add_edge('Node1', 'Node2', weight=9, something='isSomething')
-        G.add_edge('Node2', 'Node3', weight=4, something='isNotSomething')
-        G.add_edge('Node1', 'Node2')
+        G.add_node("Node1", node_data="foobar")
+        G.add_node("Node3", node_data="bar")
+        G.add_node("Node4")
+        G.add_edge("Node1", "Node2", weight=9, something="isSomething")
+        G.add_edge("Node2", "Node3", weight=4, something="isNotSomething")
+        G.add_edge("Node1", "Node2")
         d = jit_data(G)
         K = jit_graph(json.loads(d))
         assert nx.is_isomorphic(G, K)
diff --git a/networkx/readwrite/json_graph/tests/test_node_link.py b/networkx/readwrite/json_graph/tests/test_node_link.py
index 75fe142e..e5773d26 100644
--- a/networkx/readwrite/json_graph/tests/test_node_link.py
+++ b/networkx/readwrite/json_graph/tests/test_node_link.py
@@ -5,7 +5,6 @@ from networkx.readwrite.json_graph import node_link_data, node_link_graph
 
 
 class TestNodeLink:
-
     def test_graph(self):
         G = nx.path_graph(4)
         H = node_link_graph(node_link_data(G))
@@ -13,22 +12,22 @@ class TestNodeLink:
 
     def test_graph_attributes(self):
         G = nx.path_graph(4)
-        G.add_node(1, color='red')
+        G.add_node(1, color="red")
         G.add_edge(1, 2, width=7)
-        G.graph[1] = 'one'
-        G.graph['foo'] = 'bar'
+        G.graph[1] = "one"
+        G.graph["foo"] = "bar"
 
         H = node_link_graph(node_link_data(G))
-        assert H.graph['foo'] == 'bar'
-        assert H.nodes[1]['color'] == 'red'
-        assert H[1][2]['width'] == 7
+        assert H.graph["foo"] == "bar"
+        assert H.nodes[1]["color"] == "red"
+        assert H[1][2]["width"] == 7
 
         d = json.dumps(node_link_data(G))
         H = node_link_graph(json.loads(d))
-        assert H.graph['foo'] == 'bar'
-        assert H.graph['1'] == 'one'
-        assert H.nodes[1]['color'] == 'red'
-        assert H[1][2]['width'] == 7
+        assert H.graph["foo"] == "bar"
+        assert H.graph["1"] == "one"
+        assert H.nodes[1]["color"] == "red"
+        assert H[1][2]["width"] == 7
 
     def test_digraph(self):
         G = nx.DiGraph()
@@ -37,11 +36,11 @@ class TestNodeLink:
 
     def test_multigraph(self):
         G = nx.MultiGraph()
-        G.add_edge(1, 2, key='first')
-        G.add_edge(1, 2, key='second', color='blue')
+        G.add_edge(1, 2, key="first")
+        G.add_edge(1, 2, key="second", color="blue")
         H = node_link_graph(node_link_data(G))
         nx.is_isomorphic(G, H)
-        assert H[1][2]['second']['color'] == 'blue'
+        assert H[1][2]["second"]["color"] == "blue"
 
     def test_graph_with_tuple_nodes(self):
         G = nx.Graph()
@@ -51,7 +50,7 @@ class TestNodeLink:
         dd = json.loads(dumped_d)
         H = node_link_graph(dd)
         assert H.nodes[(0, 0)] == G.nodes[(0, 0)]
-        assert H[(0, 0)][(1, 0)]['color'] == [255, 255, 0]
+        assert H[(0, 0)][(1, 0)]["color"] == [255, 255, 0]
 
     def test_unicode_keys(self):
         q = "qualité"
@@ -66,32 +65,40 @@ class TestNodeLink:
     def test_exception(self):
         with pytest.raises(nx.NetworkXError):
             G = nx.MultiDiGraph()
-            attrs = dict(name='node', source='node', target='node', key='node')
+            attrs = dict(name="node", source="node", target="node", key="node")
             node_link_data(G, attrs)
 
     def test_string_ids(self):
         q = "qualité"
         G = nx.DiGraph()
-        G.add_node('A')
+        G.add_node("A")
         G.add_node(q)
-        G.add_edge('A', q)
+        G.add_edge("A", q)
         data = node_link_data(G)
-        assert data['links'][0]['source'] == 'A'
-        assert data['links'][0]['target'] == q
+        assert data["links"][0]["source"] == "A"
+        assert data["links"][0]["target"] == q
         H = node_link_graph(data)
         assert nx.is_isomorphic(G, H)
 
     def test_custom_attrs(self):
         G = nx.path_graph(4)
-        G.add_node(1, color='red')
+        G.add_node(1, color="red")
         G.add_edge(1, 2, width=7)
-        G.graph[1] = 'one'
-        G.graph['foo'] = 'bar'
+        G.graph[1] = "one"
+        G.graph["foo"] = "bar"
 
-        attrs = dict(source='c_source', target='c_target', name='c_id', key='c_key', link='c_links')
+        attrs = dict(
+            source="c_source",
+            target="c_target",
+            name="c_id",
+            key="c_key",
+            link="c_links",
+        )
 
-        H = node_link_graph(node_link_data(G, attrs=attrs), multigraph=False, attrs=attrs)
+        H = node_link_graph(
+            node_link_data(G, attrs=attrs), multigraph=False, attrs=attrs
+        )
         assert nx.is_isomorphic(G, H)
-        assert H.graph['foo'] == 'bar'
-        assert H.nodes[1]['color'] == 'red'
-        assert H[1][2]['width'] == 7
+        assert H.graph["foo"] == "bar"
+        assert H.nodes[1]["color"] == "red"
+        assert H[1][2]["width"] == 7
diff --git a/networkx/readwrite/json_graph/tests/test_tree.py b/networkx/readwrite/json_graph/tests/test_tree.py
index 5decfaf3..8deda52b 100644
--- a/networkx/readwrite/json_graph/tests/test_tree.py
+++ b/networkx/readwrite/json_graph/tests/test_tree.py
@@ -5,10 +5,9 @@ from networkx.readwrite.json_graph import tree_data, tree_graph
 
 
 class TestTree:
-
     def test_graph(self):
         G = nx.DiGraph()
-        G.add_nodes_from([1, 2, 3], color='red')
+        G.add_nodes_from([1, 2, 3], color="red")
         G.add_edge(1, 2, foo=7)
         G.add_edge(1, 3, foo=10)
         G.add_edge(3, 4, foo=10)
@@ -17,20 +16,20 @@ class TestTree:
 
     def test_graph_attributes(self):
         G = nx.DiGraph()
-        G.add_nodes_from([1, 2, 3], color='red')
+        G.add_nodes_from([1, 2, 3], color="red")
         G.add_edge(1, 2, foo=7)
         G.add_edge(1, 3, foo=10)
         G.add_edge(3, 4, foo=10)
         H = tree_graph(tree_data(G, 1))
-        assert H.nodes[1]['color'] == 'red'
+        assert H.nodes[1]["color"] == "red"
 
         d = json.dumps(tree_data(G, 1))
         H = tree_graph(json.loads(d))
-        assert H.nodes[1]['color'] == 'red'
+        assert H.nodes[1]["color"] == "red"
 
     def test_exception(self):
         with pytest.raises(nx.NetworkXError):
             G = nx.MultiDiGraph()
             G.add_node(0)
-            attrs = dict(id='node', children='node')
+            attrs = dict(id="node", children="node")
             tree_data(G, 0, attrs)
diff --git a/networkx/readwrite/json_graph/tree.py b/networkx/readwrite/json_graph/tree.py
index 70ca186f..30ef1b53 100644
--- a/networkx/readwrite/json_graph/tree.py
+++ b/networkx/readwrite/json_graph/tree.py
@@ -1,9 +1,9 @@
 from itertools import chain
 import networkx as nx
 
-__all__ = ['tree_data', 'tree_graph']
+__all__ = ["tree_data", "tree_graph"]
 
-_attrs = dict(id='id', children='children')
+_attrs = dict(id="id", children="children")
 
 
 def tree_data(G, root, attrs=_attrs):
@@ -66,10 +66,10 @@ def tree_data(G, root, attrs=_attrs):
     if not G.is_directed():
         raise TypeError("G is not directed.")
 
-    id_ = attrs['id']
-    children = attrs['children']
+    id_ = attrs["id"]
+    children = attrs["children"]
     if id_ == children:
-        raise nx.NetworkXError('Attribute names are not unique.')
+        raise nx.NetworkXError("Attribute names are not unique.")
 
     def add_children(n, G):
         nbrs = G[n]
@@ -123,8 +123,8 @@ def tree_graph(data, attrs=_attrs):
     tree_graph, node_link_data, adjacency_data
     """
     graph = nx.DiGraph()
-    id_ = attrs['id']
-    children = attrs['children']
+    id_ = attrs["id"]
+    children = attrs["children"]
 
     def add_children(parent, children_):
         for data in children_:
@@ -133,14 +133,14 @@ def tree_graph(data, attrs=_attrs):
             grandchildren = data.get(children, [])
             if grandchildren:
                 add_children(child, grandchildren)
-            nodedata = {str(k): v for k, v in data.items()
-                            if k != id_ and k != children}
+            nodedata = {
+                str(k): v for k, v in data.items() if k != id_ and k != children
+            }
             graph.add_node(child, **nodedata)
 
     root = data[id_]
     children_ = data.get(children, [])
-    nodedata = {str(k): v for k, v in data.items()
-                    if k != id_ and k != children}
+    nodedata = {str(k): v for k, v in data.items() if k != id_ and k != children}
     graph.add_node(root, **nodedata)
     add_children(root, children_)
     return graph