.

wcfs/internal/xbtree.py

@@ -240,6 +240,8 @@ def Restructure(ztree, newStructure):
     # Bj ∈ RNv is mapped into Ai ∈ RZv such that that sum_j D(A_i, Bj) is minimal.
     # it is used to associate nodes in tnew to ztree nodes.
     def assign(RZv, RNv):
+        print()
+        print('assign %s <- %s' % (RZv, RNv))
         for rzn in RZv:
             assert isinstance(rzn, _NodeInRange)
             assert isinstance(rzn.node, (ztreeType, zbucketType))
@@ -268,8 +270,10 @@ def Restructure(ztree, newStructure):
         # assignments more efficiently taking that Av and Bv are key↑ and the
         # property of D function so that if B2 > B1 (all keys in B2 > all keys
         # in B1) and A < B1.hi, then D(B2, A) > D(B1, A).
+        print()
         print(C)
         jv, iv = scipy.optimize.linear_sum_assignment(C)
+        print(jv, iv)
         for (j,i) in zip(jv, iv):
             RNv[j].node.Z = RZv[i].node
 
@@ -278,6 +282,7 @@ def Restructure(ztree, newStructure):
         # to newly created Z nodes.
         for j2 in range(len(RNv)):
             if j2 not in jv:
+                print('\n\n\nXXX create new @%d\n\n\n' % j2)
                 n = RNv[j2].node
                 assert n.Z is None
                 assert isinstance(n, (Tree,Bucket))
@@ -349,8 +354,10 @@ def Restructure(ztree, newStructure):
     assert len(rbucketv) > 0
     for i in range(len(rbucketv)-1):
         assert rbucketv[i].range.khi <= rbucketv[i+1].klo
-        rbucketv[i].node.next_bucket = rbucketv[i+1].node
+        rbucketv[i]  .node.next_bucket = rbucketv[i+1].node
+        rbucketv[i+1].node.prev_bucket = rbucketv[i]  .node
     rbucketv[-1].node.next_bucket = None
+    rbucketv[0] .node.prev_bucket = None
 
     # associate every bucket to zbucket
     assign(zrbucketv, rbucketv)
@@ -361,18 +368,24 @@ def Restructure(ztree, newStructure):
     for rnodev in rlevelv:
         for rn in rnodev:
             node = rn.node
-            assert isinstance(node, Tree)   # buckets were filtered out to rbucketv
+            assert isinstance(node, Tree), node # buckets were filtered out to rbucketv
             znode = node.Z
 
             # https://github.com/zopefoundation/BTrees/blob/4.5.0-1-gc8bf24e/BTrees/BTreeTemplate.c#L1087
+            zstate = unset = object()
             if len(node.keyv) == 0:
                 child = node.children[0]
                 if isinstance(child, Bucket):
-                    if len(child.keyv) == 0:
-                        panic("TODO: empty tree")
-                    if child.Z._p_oid is None:
-                        panic("TODO: tree with bucket without oid")
+                    # empty bucket noone links to
+                    if len(child.keyv) == 0 and child.prev_bucket is None:
+                        zstate = None   # -> empty tree
 
+                    # tree with single bucket noone links to
+                    elif child.Z._p_oid is None and child.prev_bucket is None:
+                        zstate = ((child.Z.__getstate__(),),)   # tree with bucket without oid
+
+            if zstate is unset:
+                # normal tree node
                 zstate = ()
                 assert len(node.children) == len(node.keyv) + 1
                 zstate += node.children[0]