add option to view specific attributes in G.nodes()

2 files changed, 45 insertions, 16 deletions

diff --git a/networkx/classes/graph.py b/networkx/classes/graph.py
index b12b960a..6d785933 100644
--- a/networkx/classes/graph.py
+++ b/networkx/classes/graph.py
@@ -608,22 +608,30 @@ class Graph(object):
             except KeyError:
                 pass
 
-    def nodes(self, data=False):
+    def nodes(self, data=False, default=None):
         """Returns an iterator over the nodes.
 
         Parameters
         ----------
         data : boolean, optional (default=False)
-               If ``False``, the iterator returns nodes.  If ``True``,
-               the iterator return a two-tuple of node and node data
-               dictionary.
+            If ``False``, the iterator returns nodes.  If ``True``,
+            the iterator returns a two-tuple of node and node data
+            dictionary. ``data`` can also be a specific node attribute from
+            node data dictionary, if ``data`` is an attribute, the iterator
+            returns a two-tuple of node and value of node attribute.
+
+        default : value, optional (default=None)
+            Value used for nodes that dont have the requested attribute.
+            Only relevant if data is not True or False.
 
         Returns
         -------
         iterator
             An iterator over nodes, or if ``data`` is ``True``, an
             iterator over two-tuples of the form ``(node, node data
-            dictionary)``.
+            dictionary)``, or if ``data`` is an attribute from the node
+            data dictionary, an iterator over two-tuples of the form ``(node,
+            attribute value)``
 
         Notes
         -----
@@ -632,7 +640,8 @@ class Graph(object):
 
         Examples
         --------
-        There are two simple ways of getting a list of all nodes in the graph::
+        There are two simple ways of getting a list of all nodes in the graph:
+
         >>> G = nx.Graph()
         >>> G.add_nodes_from(range(3))
         >>> list(G.nodes())
@@ -640,16 +649,31 @@ class Graph(object):
         >>> list(G)
         [0, 1, 2]
 
-        To get the node data along with the nodes::
+        To get the node data along with the nodes:
+
         >>> G.add_node(1, time='5pm')
         >>> G.node[0]['foo'] = 'bar'
         >>> list(G.nodes(data=True))
         [(0, {'foo': 'bar'}), (1, {'time': '5pm'}), (2, {})]
-
+        >>> list(G.nodes(data='foo'))
+        [(0, 'bar'), (1, None), (2, None)]
+        >>> list(G.nodes(data='time'))
+        [(0, None), (1, '5pm'), (2, None)]
+        >>> list(G.nodes(data='time', default='Not Available'))
+        [(0, 'Not Available'), (1, '5pm'), (2, 'Not Available')]
         """
-        if data:
-            return iter(self.node.items())
-        return iter(self.node)
+        ndict = self.node.items()
+        if data is True:
+            for n, ddict in ndict:
+                yield (n, ddict)
+        elif data is not False:
+            for n, ddict in ndict:
+                d = ddict[data] if data in ddict else default
+                yield (n, d)
+        else:
+            for n in self.node:
+                yield n
+
 
     def number_of_nodes(self):
         """Return the number of nodes in the graph.
diff --git a/networkx/classes/tests/test_graph.py b/networkx/classes/tests/test_graph.py
index 982c96ea..c54b4965 100644
--- a/networkx/classes/tests/test_graph.py
+++ b/networkx/classes/tests/test_graph.py
@@ -1,5 +1,5 @@
-#!/usr/bin/env python
-from nose.tools import *
+from nose.tools import (assert_equal, assert_raises, assert_true, raises,
+                        assert_not_equal)
 import networkx
 
 class BaseGraphTester(object):
@@ -324,14 +324,19 @@ class BaseAttrGraphTester(BaseGraphTester):
         assert_equal(H.graph['foo'], 'bar')
 
     def test_node_attr(self):
-        G=self.K3
-        G.add_node(1,foo='bar')
+        G = self.K3
+        G.add_node(1, foo='bar')
         assert_equal(list(G.nodes()), [0, 1, 2])
         assert_equal(list(G.nodes(data=True)),
                      [(0, {}), (1, {'foo':'bar'}), (2, {})])
-        G.node[1]['foo']='baz'
+        G.node[1]['foo'] = 'baz'
         assert_equal(list(G.nodes(data=True)),
                      [(0, {}), (1, {'foo':'baz'}), (2, {})])
+        assert_equal(list(G.nodes(data='foo')),
+                     [(0, None), (1, 'baz'), (2, None)])
+        assert_equal(list(G.nodes(data='foo', default='bar')),
+                     [(0, 'bar'), (1, 'baz'), (2, 'bar')])
+
 
     def test_node_attr2(self):
         G=self.K3