Minor docstring touchups and test refactor for `is_path` (#5967)

* Touch up docstring.

* Condense conditional.

* Minor refactor of ispath test - parametrize and rm redundant.

* Add release note.

* Update networkx/classes/function.py

Co-authored-by: Dan Schult <dschult@colgate.edu>

Co-authored-by: Dan Schult <dschult@colgate.edu>

4 files changed, 51 insertions, 19 deletions

diff --git a/doc/release/index.rst b/doc/release/index.rst
index 5def917a..e7f9b7cd 100644
--- a/doc/release/index.rst
+++ b/doc/release/index.rst
@@ -15,6 +15,7 @@ period.
    :maxdepth: 2
 
    release_dev
+   release_2.8.7
    release_2.8.6
    release_2.8.5
    release_2.8.4
diff --git a/doc/release/release_2.8.7.rst b/doc/release/release_2.8.7.rst
new file mode 100644
index 00000000..9f3cf3ca
--- /dev/null
+++ b/doc/release/release_2.8.7.rst
@@ -0,0 +1,35 @@
+NetworkX 2.8.7
+==============
+
+Release date: TBD
+
+Supports Python 3.8, 3.9, and 3.10.
+
+NetworkX is a Python package for the creation, manipulation, and study of the
+structure, dynamics, and functions of complex networks.
+
+For more information, please visit our `website <https://networkx.org/>`_
+and our :ref:`gallery of examples <examples_gallery>`.
+Please send comments and questions to the `networkx-discuss mailing list
+<http://groups.google.com/group/networkx-discuss>`_.
+
+Highlights
+----------
+
+Minor documentation and bug fixes.
+
+Merged PRs
+----------
+
+
+Improvements
+------------
+
+- [`#5943 <https://github.com/networkx/networkx/pull/5943>`_]
+  ``is_path`` used to raise a `KeyError` when the ``path`` argument contained
+  a node that was not in the Graph. The behavior has been updated so that
+  ``is_path`` returns `False` in this case rather than raising the exception.
+
+Contributors
+------------
+
diff --git a/networkx/classes/function.py b/networkx/classes/function.py
index a0807942..3750fd11 100644
--- a/networkx/classes/function.py
+++ b/networkx/classes/function.py
@@ -1289,19 +1289,17 @@ def is_path(G, path):
     G : graph
         A NetworkX graph.
 
-    path: list
-        A list of node labels which defines the path to traverse
+    path : list
+        A list of nodes which defines the path to traverse
 
     Returns
     -------
-    isPath: bool
-        A boolean representing whether or not the path exists
+    bool
+        True if `path` is a valid path in `G`
 
     """
     for node, nbr in nx.utils.pairwise(path):
-        if node not in G:
-            return False
-        if nbr not in G[node]:
+        if (node not in G) or (nbr not in G[node]):
             return False
     return True
 
diff --git a/networkx/classes/tests/test_function.py b/networkx/classes/tests/test_function.py
index df17f200..c738ab58 100644
--- a/networkx/classes/tests/test_function.py
+++ b/networkx/classes/tests/test_function.py
@@ -768,19 +768,17 @@ def test_pathweight():
         pytest.raises(nx.NetworkXNoPath, nx.path_weight, graph, invalid_path, "cost")
 
 
-def test_ispath():
+@pytest.mark.parametrize(
+    "G", (nx.Graph(), nx.DiGraph(), nx.MultiGraph(), nx.MultiDiGraph())
+)
+def test_ispath(G):
+    G.add_edges_from([(1, 2), (2, 3), (1, 2), (3, 4)])
     valid_path = [1, 2, 3, 4]
-    invalid_path = [1, 2, 4, 3]
-    another_invalid_path = [1, 2, 3, 4, 5]
-    yet_another_invalid_path = [1, 2, 5, 3, 4]
-    graphs = [nx.Graph(), nx.DiGraph(), nx.MultiGraph(), nx.MultiDiGraph()]
-    edges = [(1, 2), (2, 3), (1, 2), (3, 4)]
-    for graph in graphs:
-        graph.add_edges_from(edges)
-        assert nx.is_path(graph, valid_path)
-        assert not nx.is_path(graph, invalid_path)
-        assert not nx.is_path(graph, another_invalid_path)
-        assert not nx.is_path(graph, yet_another_invalid_path)
+    invalid_path = [1, 2, 4, 3]  # wrong node order
+    another_invalid_path = [1, 2, 3, 4, 5]  # contains node not in G
+    assert nx.is_path(G, valid_path)
+    assert not nx.is_path(G, invalid_path)
+    assert not nx.is_path(G, another_invalid_path)
 
 
 @pytest.mark.parametrize("G", (nx.Graph(), nx.DiGraph()))