diff --git a/planetstack/observer/toposort.py b/planetstack/observer/toposort.py
new file mode 100755
index 0000000..34bf6f5
--- /dev/null
+++ b/planetstack/observer/toposort.py
@@ -0,0 +1,48 @@
+#!/usr/bin/python
+
+import time
+import traceback
+import commands
+import threading
+import json
+
+from datetime import datetime
+from collections import defaultdict
+
+def toposort(g, steps):
+	reverse = {}
+
+	for k,v in g.items():
+		for rk in v:
+			try:
+				reverse[rk].append(k)
+			except:
+				reverse[rk]=k
+
+	sources = []
+	for k,v in g.items():
+		if not reverse.has_key(k):
+			sources.append(k)
+
+
+	for k,v in reverse.iteritems():
+		if (not v):
+			sources.append(k)
+
+	order = []
+	marked = []
+	while sources:
+		n = sources.pop()
+		try:
+			for m in g[n]:
+				if m not in marked:
+					sources.append(m)
+					marked.append(m)
+		except KeyError:
+			pass
+		if (n in steps):
+			order.append(n)
+
+	return order
+
+print toposort({'a':'b','b':'c','c':'d','d':'c'},['d','c','b','a'])