Pull request to set up python3.7 testing on travis (#3054)

* Fix StopIteration handling which breaks in python 3.7

Fixes #3046

* Shift from testing py3.4 to py3.7 in travis

* Allow failures on python 3.7

* Try testing py37-dev version

1 files changed, 9 insertions, 3 deletions

diff --git a/networkx/algorithms/connectivity/edge_augmentation.py b/networkx/algorithms/connectivity/edge_augmentation.py
index 326478e8..67f8708e 100644
--- a/networkx/algorithms/connectivity/edge_augmentation.py
+++ b/networkx/algorithms/connectivity/edge_augmentation.py
@@ -813,7 +813,10 @@ def unconstrained_bridge_augmentation(G):
         A2 = [tuple(leafs)]
     else:
         # Choose an arbitrary non-leaf root
-        root = next(n for n, d in T.degree() if d > 1)
+        try:
+            root = next(n for n, d in T.degree() if d > 1)
+        except StopIteration:  # no nodes found with degree > 1
+            return
         # order the leaves of C by (induced directed) preorder
         v2 = [n for n in nx.dfs_preorder_nodes(T, root) if T.degree(n) == 1]
         # connecting first half of the leafs in pre-order to the second
@@ -954,7 +957,10 @@ def weighted_bridge_augmentation(G, avail, weight=None):
     #     nx.least_common_ancestor on the reversed Tree.
 
     # Pick an arbitrary leaf from C as the root
-    root = next(n for n in C.nodes() if C.degree(n) == 1)
+    try:
+        root = next(n for n, d in C.degree() if d == 1)
+    except StopIteration:  # no nodes found with degree == 1
+        return
     # Root C into a tree TR by directing all edges away from the root
     # Note in their paper T directs edges towards the root
     TR = nx.dfs_tree(C, root)
@@ -1230,7 +1236,7 @@ def greedy_k_edge_augmentation(G, k, avail=None, weight=None, seed=None):
 
     done = is_k_edge_connected(G, k)
     if done:
-        raise StopIteration()
+        return
     if avail is None:
         # all edges are available
         avail_uv = list(complement_edges(G))