python-ifupdown initial checkin

Ticket: CM-1438
Reviewed By: TBD
Testing Done:

- Will checkin build files after some more testing and performance
  numbers. It will go into the testing repo for 2.0

- All TODO items are part of the checked in TODO file

pkg/graph.py

@@ -0,0 +1,43 @@
+#!/usr/bin/python
+
+import logging
+from collections import deque
+
+class graph():
+
+    def __init__(self):
+        self.logger = logging.getLogger('ifupdown.' +
+                    self.__class__.__name__)
+
+    @classmethod
+    def topological_sort(cls, dependency_graph, indegrees=None):
+        S = []
+        Q = deque()
+
+        for ifname,indegree in indegrees.items():
+            if indegree == 0:
+                Q.append(ifname)
+
+        while len(Q) != 0:
+            # initialize queue
+            x = Q.popleft()
+
+            # Get dependents of x
+            dlist = dependency_graph.get(x)
+            if dlist == None or len(dlist) == 0:
+                S.append(x)
+                continue
+
+            for y in dlist:
+                indegrees[y] = indegrees.get(y) - 1
+                if indegrees.get(y) == 0:
+                    Q.append(y)
+
+            S.append(x)
+
+        # If some indegrees are non zero, we have a cycle
+        for ifname,indegree in indegrees.items():
+            if indegree != 0:
+                raise Exception('cycle found involving iface %s' %ifname)
+
+        return S