From 933d3241eb23d6857716810bedfaf56123111a6a Mon Sep 17 00:00:00 2001
From: Dan Schult <dschult@colgate.edu>
Date: Sat, 7 Jul 2018 14:07:58 -0400
Subject: [PATCH] Fix StopIteration handling which breaks in python 3.7

See #3046
---

rebase against stable release

 .../algorithms/connectivity/edge_augmentation.py     | 12 +++++++++---
 networkx/algorithms/connectivity/edge_kcomponents.py |  2 +-
 networkx/algorithms/traversal/edgedfs.py             |  2 +-
 networkx/generators/classic.py                       |  2 ++
 networkx/readwrite/sparse6.py                        | 10 ++++++++--
 5 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/networkx/algorithms/connectivity/edge_augmentation.py b/networkx/algorithms/connectivity/edge_augmentation.py
index cd8c748f..21512d7c 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))
diff --git a/networkx/algorithms/connectivity/edge_kcomponents.py b/networkx/algorithms/connectivity/edge_kcomponents.py
index 37bf61dc..f9b4364c 100644
--- a/networkx/algorithms/connectivity/edge_kcomponents.py
+++ b/networkx/algorithms/connectivity/edge_kcomponents.py
@@ -573,7 +573,7 @@ def general_k_edge_subgraphs(G, k):
     if G.number_of_nodes() < k:
         for node in G.nodes():
             yield G.subgraph([node]).copy()
-        raise StopIteration()
+        return
 
     # Intermediate results
     R0 = {G.subgraph(cc).copy() for cc in find_ccs(G)}
diff --git a/networkx/algorithms/traversal/edgedfs.py b/networkx/algorithms/traversal/edgedfs.py
index 5434057d..b9d442b6 100644
--- a/networkx/algorithms/traversal/edgedfs.py
+++ b/networkx/algorithms/traversal/edgedfs.py
@@ -152,7 +152,7 @@ def edge_dfs(G, source=None, orientation='original'):
     """
     nodes = list(G.nbunch_iter(source))
     if not nodes:
-        raise StopIteration
+        return
 
     kwds = {'data': False}
     if G.is_multigraph():
diff --git a/networkx/generators/classic.py b/networkx/generators/classic.py
index 22741a37..10710db4 100644
--- a/networkx/generators/classic.py
+++ b/networkx/generators/classic.py
@@ -54,6 +54,8 @@ __all__ = ['balanced_tree',
 # -------------------------------------------------------------------
 
 def _tree_edges(n, r):
+    if n == 0:
+        return
     # helper function for trees
     # yields edges in rooted tree at 0 with n nodes and branching ratio r
     nodes = iter(range(n))
diff --git a/networkx/readwrite/sparse6.py b/networkx/readwrite/sparse6.py
index 00ccae60..6f404ca3 100644
--- a/networkx/readwrite/sparse6.py
+++ b/networkx/readwrite/sparse6.py
@@ -163,7 +163,10 @@ def from_sparse6_bytes(string):
 
         while 1:
             if dLen < 1:
-                d = next(chunks)
+                try:
+                    d = next(chunks)
+                except StopIteration:
+                    return
                 dLen = 6
             dLen -= 1
             b = (d >> dLen) & 1  # grab top remaining bit
@@ -171,7 +174,10 @@ def from_sparse6_bytes(string):
             x = d & ((1 << dLen) - 1)  # partially built up value of x
             xLen = dLen		# how many bits included so far in x
             while xLen < k:  # now grab full chunks until we have enough
-                d = next(chunks)
+                try:
+                    d = next(chunks)
+                except StopIteration:
+                    return
                 dLen = 6
                 x = (x << 6) + d
                 xLen += 6
-- 
2.18.0