Add bootstrap model dependecies support

apps/bootstrap/utils.py

@@ -0,0 +1,40 @@
+## {{{ http://code.activestate.com/recipes/578272/ (r1)
+def toposort2(data):
+    """Dependencies are expressed as a dictionary whose keys are items
+and whose values are a set of dependent items. Output is a list of
+sets in topological order. The first set consists of items with no
+dependences, each subsequent set consists of items that depend upon
+items in the preceeding sets.
+
+>>> print '\\n'.join(repr(sorted(x)) for x in toposort2({
+...     2: set([11]),
+...     9: set([11,8]),
+...     10: set([11,3]),
+...     11: set([7,5]),
+...     8: set([7,3]),
+...     }) )
+[3, 5, 7]
+[8, 11]
+[2, 9, 10]
+
+"""
+
+    from functools import reduce
+
+    # Ignore self dependencies.
+    for k, v in data.items():
+        v.discard(k)
+    # Find all items that don't depend on anything.
+    extra_items_in_deps = reduce(set.union, data.itervalues()) - set(data.iterkeys())
+    # Add empty dependences where needed
+    data.update({item:set() for item in extra_items_in_deps})
+    while True:
+        ordered = set(item for item, dep in data.iteritems() if not dep)
+        if not ordered:
+            break
+        yield ordered
+        data = {item: (dep - ordered)
+                for item, dep in data.iteritems()
+                    if item not in ordered}
+    assert not data, "Cyclic dependencies exist among these items:\n%s" % '\n'.join(repr(x) for x in data.iteritems())
+## end of http://code.activestate.com/recipes/578272/ }}}