Merge pull request #24 from NelleV/no_edges_to_plot

plot_network fails if there is no edges to plot.

Makefile

@@ -0,0 +1,7 @@
+
+
+
+all:
+
+test:
+	py.test grave

examples/plot_layout_custom.py

@@ -5,8 +5,8 @@
 The default layouts available through Grave may not be sufficient for ones
 need. Hence, Grave also support custom layouts.
 
-
 """
+
 import numpy as np
 import networkx as nx
 import matplotlib.pyplot as plt

grave/_layout.py

@@ -1,7 +1,7 @@
 import networkx as nx
 
 
-known_layouts = {
+KNOWN_LAYOUTS = {
     "spring": nx.spring_layout,
     "circular": nx.circular_layout,
     "random": nx.random_layout,
@@ -15,6 +15,6 @@ def _apply_layout(layout, graph):
     if callable(layout):
         return layout(graph)
     elif isinstance(layout, str):
-        return known_layouts[layout](graph)
+        return KNOWN_LAYOUTS[layout](graph)
     else:
         raise ValueError("Dunno what do do with this")

grave/grave.py

@@ -71,6 +71,8 @@ def _generate_node_artist(pos, styles, *, ax):
 
 def _generate_straight_edges(edges, pos, styles, *, ax):
     N = len(edges)
+    if not N:
+        return None, None
     proto_edge = next(iter(edges))
     edge_pos = [None] * N
     edge_indx = [None] * N
@@ -84,7 +86,7 @@ def _generate_straight_edges(edges, pos, styles, *, ax):
         edge_indx[j] = (u, v)
     key_map = {'color': 'colors',
                'width': 'linewidths',
-               'style': 'linestyle'}
+               'style': 'linestyle',}
 
     renamed_properties = {key_map[k]: v
                           for k, v in properties.items()}
@@ -373,6 +375,15 @@ def plot_network(graph, layout="spring",
     ----------
 
     graph : networkx graph object
+
+    layout : string or callable, optional, default: "spring"
+        Specifies the type of layout to use for plotting.
+        It must be one of "spring", "circular", "random", "kamada_kawai",
+        "shell", "spectral", or a callable.
+        If a callable is given, it is used to compute the 2D coordinates from
+        the graph object, and should return a FIXME.
+        
+
     """
     if node_style is None:
         node_style = {}

grave/tests/test_grave.py

@@ -2,14 +2,20 @@
 
 import networkx as nx
 
+from grave import plot_network
 import matplotlib as mpl
 mpl.use('PS', warn=False)
+
 import matplotlib.pyplot as plt
 plt.rcParams['text.usetex'] = False
 
-from grave import plot_network
+
+def test_smoke_graph():
+    graph = nx.barbell_graph(10, 14)
+    plot_network(graph)
 
 
-def test_empty_graph():
-    G = nx.barbell_graph(10, 14)
-    plot_network(G)
+def test_graph_no_edges():
+    graph = nx.Graph()
+    graph.add_node(0)
+    plot_network(graph)