RenderTree, LevelOrderIter etc access more child attributes than necessary when restricting maxlevel

[wimglenn]

I am using anytree in johnnydep for rendering package dependencies. In my case, accessing the children attribute of a node instance creates the children dynamically, i.e. they are generated lazily on demand. There's a good reason for this- it entails a network request to get the package metadata, so we would like to avoid it if it won't actually be used (i.e. we never iterate to that depth).

That's when I found this issue- bounding the iterators such as LevelOrderIter and RenderTree by passing maxlevel still accesses more children attributes than necessary.

Here is an example reproducing the issue. If we use the example tree from the docs, where the full tree is:

Udo
├── Marc
│   └── Lian
└── Dan
    ├── Jet
    ├── Jan
    └── Joe

But pruning with maxlevel=2 it is just:

Udo
├── Marc
└── Dan

When we reveal "children" attribute access by overriding __getattribute__:

from anytree import Node as _Node, RenderTree, LevelOrderIter

maxlevel = 2

class Node(_Node):
    def __getattribute__(self, name):
        if name == "children":
            print("__getattribute__ children of node", self.name)
        return _Node.__getattribute__(self, name)

udo = Node("Udo")
marc = Node("Marc", parent=udo)
lian = Node("Lian", parent=marc)
dan = Node("Dan", parent=udo)
jet = Node("Jet", parent=dan)
jan = Node("Jan", parent=dan)
joe = Node("Joe", parent=dan)

for pre, fill, node in RenderTree(udo, maxlevel=maxlevel):
    print("%s%s" % (pre, node.name))

print()
for node in LevelOrderIter(udo, maxlevel=maxlevel):
    print(node)

I get this output:

Udo
__getattribute__ children of node Udo
├── Marc
__getattribute__ children of node Marc
└── Dan
__getattribute__ children of node Dan

Node('/Udo')
__getattribute__ children of node Udo
Node('/Udo/Marc')
__getattribute__ children of node Marc
Node('/Udo/Dan')
__getattribute__ children of node Dan

The children of Marc and Dan are accessed, even though they aren't used.

Would it be possible to refactor the iterators so that they access no more children than they strictly need to?

[c0fec0de]

Fixed in 2.10.0

[wimglenn]

Thanks! Link for posterity 2e803f6