diff --git a/pisi/graph.py b/pisi/graph.py
new file mode 100644
index 00000000..30d3cf19
--- /dev/null
+++ b/pisi/graph.py
@@ -0,0 +1,68 @@
+# the most simple minded digraph class ever
+
+class digraph(object):
+
+    def __init__(self):
+        self.__v = set()
+        self.__adj = {}
+        self.__vdata = {}
+        #self.__edata = {}
+
+    def add_vertex(u, data = None):
+        assert not u in self.__v
+        self.__v.add(u)
+        if data!=None:
+            self.__vdata[u] = data
+
+    def add_edge(u, v, edata = None):
+        self.__adj[u].add(u)
+        #if edata != None:
+
+    def set_vertex_data(u, data):
+        self.__vdata[u] = data
+
+    def vertex_data(u):
+        self.__vdata[u]
+
+    def has_vertex(u):
+        return u in self.__v
+
+    def has_edge(u,v):
+        if u in self.__v:
+            return v in self.__adj[u]
+        else:
+            return False
+
+    def adj(u):
+        return self.__adj[u]
+
+    def dfs(finish_hook = None):
+        self.color = {}
+        self.p = {}
+        self.d = {}
+        self.f = {}
+        for u in self.__v:
+            self.color[u] = 'w'
+            self.p[u] = None
+        self.time = 0
+        for u in self.__v:
+            if color[u] = 'w':
+                dfs_visit(u)
+
+    def dfs_visit(u, finish_hook):
+        self.color[u] = 'g'
+        self.d[u] = self.time = self.time + 1
+        for v in self.adj(u):
+            if self.color[v] = 'w':
+                self.p[v] = u
+                dfs_visit(v)
+        self.color[u] = black
+        if finish_hook != None:
+            finish_hook(u)
+        self.f[u] = self.time = self.time + 1
+
+    def topological_sort():
+        l = []
+        dfs(lambda u: l.append(u))
+        return l
+