DEP : adding not_implemented_for("multigraph”) to k_core, k_shell, k_crust and k_corona

doc/developer/deprecations.rst

@@ -68,3 +68,4 @@ Version 3.5
 ~~~~~~~~~~~
 * Remove ``all_triplets`` from ``algorithms/triads.py``
 * Remove ``random_triad`` from ``algorithms/triad.py``.
+* Add `not_implemented_for("multigraph”)` decorator to ``k_core``, ``k_shell``, ``k_crust`` and ``k_corona`` functions.

networkx/algorithms/core.py

@@ -154,6 +154,9 @@ def k_core(G, k=None, core_number=None):
 
     A k-core is a maximal subgraph that contains nodes of degree `k` or more.
 
+    .. deprecated:: 3.3
+       `k_core` will not accept `MultiGraph` objects in version 3.5.
+
     Parameters
     ----------
     G : NetworkX graph
@@ -202,6 +205,19 @@ def k_core(G, k=None, core_number=None):
        https://arxiv.org/abs/cs.DS/0310049
     """
 
+    import warnings
+
+    if G.is_multigraph():
+        warnings.warn(
+            (
+                "\n\n`k_core` will not accept `MultiGraph` objects in version 3.5.\n"
+                "Convert it to an undirected graph instead, using::\n\n"
+                "\tG = nx.Graph(G)\n"
+            ),
+            category=DeprecationWarning,
+            stacklevel=5,
+        )
+
     def k_filter(v, k, c):
         return c[v] >= k
 
@@ -215,6 +231,9 @@ def k_shell(G, k=None, core_number=None):
     The k-shell is the subgraph induced by nodes with core number k.
     That is, nodes in the k-core that are not in the (k+1)-core.
 
+    .. deprecated:: 3.3
+       `k_shell` will not accept `MultiGraph` objects in version 3.5.
+
     Parameters
     ----------
     G : NetworkX graph
@@ -268,6 +287,19 @@ def k_shell(G, k=None, core_number=None):
        http://www.pnas.org/content/104/27/11150.full
     """
 
+    import warnings
+
+    if G.is_multigraph():
+        warnings.warn(
+            (
+                "\n\n`k_shell` will not accept `MultiGraph` objects in version 3.5.\n"
+                "Convert it to an undirected graph instead, using::\n\n"
+                "\tG = nx.Graph(G)\n"
+            ),
+            category=DeprecationWarning,
+            stacklevel=5,
+        )
+
     def k_filter(v, k, c):
         return c[v] == k
 
@@ -281,6 +313,9 @@ def k_crust(G, k=None, core_number=None):
     The k-crust is the graph G with the edges of the k-core removed
     and isolated nodes found after the removal of edges are also removed.
 
+    .. deprecated:: 3.3
+       `k_crust` will not accept `MultiGraph` objects in version 3.5.
+
     Parameters
     ----------
     G : NetworkX graph
@@ -330,6 +365,20 @@ def k_crust(G, k=None, core_number=None):
        and Eran Shir, PNAS  July 3, 2007   vol. 104  no. 27  11150-11154
        http://www.pnas.org/content/104/27/11150.full
     """
+
+    import warnings
+
+    if G.is_multigraph():
+        warnings.warn(
+            (
+                "\n\n`k_crust` will not accept `MultiGraph` objects in version 3.5.\n"
+                "Convert it to an undirected graph instead, using::\n\n"
+                "\tG = nx.Graph(G)\n"
+            ),
+            category=DeprecationWarning,
+            stacklevel=5,
+        )
+
     # Default for k is one less than in _core_subgraph, so just inline.
     #    Filter is c[v] <= k
     if core_number is None:
@@ -347,6 +396,9 @@ def k_corona(G, k, core_number=None):
     The k-corona is the subgraph of nodes in the k-core which have
     exactly k neighbours in the k-core.
 
+    .. deprecated:: 3.3
+       `k_corona` will not accept `MultiGraph` objects in version 3.5.
+
     Parameters
     ----------
     G : NetworkX graph
@@ -395,6 +447,19 @@ def k_corona(G, k, core_number=None):
        http://link.aps.org/doi/10.1103/PhysRevE.73.056101
     """
 
+    import warnings
+
+    if G.is_multigraph():
+        warnings.warn(
+            (
+                "\n\n`k_corona` will not accept `MultiGraph` objects in version 3.5.\n"
+                "Convert it to an undirected graph instead, using::\n\n"
+                "\tG = nx.Graph(G)\n"
+            ),
+            category=DeprecationWarning,
+            stacklevel=5,
+        )
+
     def func(v, k, c):
         return c[v] == k and k == sum(1 for w in G[v] if c[w] >= k)
 

networkx/algorithms/tests/test_core.py

@@ -69,6 +69,15 @@ def test_core_number2(self):
         assert nodes_equal(nodes_by_core[1], [1, 3])
         assert nodes_equal(nodes_by_core[2], [2, 4, 5, 6])
 
+    def test_core_number_multigraph(self):
+        G = nx.complete_graph(3)
+        G = nx.MultiGraph(G)
+        G.add_edge(1, 2)
+        with pytest.raises(
+            nx.NetworkXNotImplemented, match="not implemented for multigraph type"
+        ):
+            nx.core_number(G)
+
     def test_core_number_self_loop(self):
         G = nx.cycle_graph(3)
         G.add_edge(0, 0)
@@ -104,6 +113,12 @@ def test_k_core(self):
         k_core_subgraph = nx.k_core(self.H, k=2)
         assert sorted(k_core_subgraph.nodes()) == [2, 4, 5, 6]
 
+    def test_k_core_multigraph(self):
+        core_number = nx.core_number(self.H)
+        H = nx.MultiGraph(self.H)
+        with pytest.deprecated_call():
+            nx.k_core(H, k=0, core_number=core_number)
+
     def test_main_crust(self):
         main_crust_subgraph = nx.k_crust(self.H)
         assert sorted(main_crust_subgraph.nodes()) == [0, 1, 3]
@@ -119,6 +134,12 @@ def test_k_crust(self):
         k_crust_subgraph = nx.k_crust(self.H, k=0)
         assert sorted(k_crust_subgraph.nodes()) == [0]
 
+    def test_k_crust_multigraph(self):
+        core_number = nx.core_number(self.H)
+        H = nx.MultiGraph(self.H)
+        with pytest.deprecated_call():
+            nx.k_crust(H, k=0, core_number=core_number)
+
     def test_main_shell(self):
         main_shell_subgraph = nx.k_shell(self.H)
         assert sorted(main_shell_subgraph.nodes()) == [2, 4, 5, 6]
@@ -134,6 +155,12 @@ def test_k_shell(self):
         k_shell_subgraph = nx.k_shell(self.H, k=0)
         assert sorted(k_shell_subgraph.nodes()) == [0]
 
+    def test_k_shell_multigraph(self):
+        core_number = nx.core_number(self.H)
+        H = nx.MultiGraph(self.H)
+        with pytest.deprecated_call():
+            nx.k_shell(H, k=0, core_number=core_number)
+
     def test_k_corona(self):
         # k=0
         k_corona_subgraph = nx.k_corona(self.H, k=2)
@@ -145,6 +172,12 @@ def test_k_corona(self):
         k_corona_subgraph = nx.k_corona(self.H, k=0)
         assert sorted(k_corona_subgraph.nodes()) == [0]
 
+    def test_k_corona_multigraph(self):
+        core_number = nx.core_number(self.H)
+        H = nx.MultiGraph(self.H)
+        with pytest.deprecated_call():
+            nx.k_corona(H, k=0, core_number=core_number)
+
     def test_k_truss(self):
         # k=-1
         k_truss_subgraph = nx.k_truss(self.G, -1)
@@ -168,6 +201,24 @@ def test_k_truss(self):
         k_truss_subgraph = nx.k_truss(self.G, 5)
         assert sorted(k_truss_subgraph.nodes()) == []
 
+    def test_k_truss_digraph(self):
+        G = nx.complete_graph(3)
+        G = nx.DiGraph(G)
+        G.add_edge(2, 1)
+        with pytest.raises(
+            nx.NetworkXNotImplemented, match="not implemented for directed type"
+        ):
+            nx.k_truss(G, k=1)
+
+    def test_k_truss_multigraph(self):
+        G = nx.complete_graph(3)
+        G = nx.MultiGraph(G)
+        G.add_edge(1, 2)
+        with pytest.raises(
+            nx.NetworkXNotImplemented, match="not implemented for multigraph type"
+        ):
+            nx.k_truss(G, k=1)
+
     def test_k_truss_self_loop(self):
         G = nx.cycle_graph(3)
         G.add_edge(0, 0)
@@ -188,6 +239,24 @@ def test_onion_layers(self):
         assert nodes_equal(nodes_by_layer[4], [1, 2, 4, 5, 6, 8])
         assert nodes_equal(nodes_by_layer[5], [3, 7])
 
+    def test_onion_digraph(self):
+        G = nx.complete_graph(3)
+        G = nx.DiGraph(G)
+        G.add_edge(2, 1)
+        with pytest.raises(
+            nx.NetworkXNotImplemented, match="not implemented for directed type"
+        ):
+            nx.onion_layers(G)
+
+    def test_onion_multigraph(self):
+        G = nx.complete_graph(3)
+        G = nx.MultiGraph(G)
+        G.add_edge(1, 2)
+        with pytest.raises(
+            nx.NetworkXNotImplemented, match="not implemented for multigraph type"
+        ):
+            nx.onion_layers(G)
+
     def test_onion_self_loop(self):
         G = nx.cycle_graph(3)
         G.add_edge(0, 0)

networkx/conftest.py

@@ -133,6 +133,16 @@ def set_warnings():
     warnings.filterwarnings(
         "ignore", category=DeprecationWarning, message="\n\nrandom_triad"
     )
+    warnings.filterwarnings("ignore", category=DeprecationWarning, message="\n\nk_core")
+    warnings.filterwarnings(
+        "ignore", category=DeprecationWarning, message="\n\nk_shell"
+    )
+    warnings.filterwarnings(
+        "ignore", category=DeprecationWarning, message="\n\nk_crust"
+    )
+    warnings.filterwarnings(
+        "ignore", category=DeprecationWarning, message="\n\nk_corona"
+    )
 
 
 @pytest.fixture(autouse=True)