I have a problem in which I am trying to construct a tree (not always binary). Given a node at any depth of the tree, I wish to be able to add N new nodes to a children list attribute. The following example code results in child nodes being recursivley generated and each new child node in self.children contains a copy of itself.
class Node:
# Constructor to create a Node
def __init__(self, data, children=[]):
self.value = data
self.children = children
@classmethod
def spawn(cls, data):
return cls(data)
def spawn_child(self, data):
child = self.spawn(data)
self.children.append(child)
def max_depth(node):
if len(node.children) == 0:
return 0
else:
depths = []
for child in node.children:
depths.append(max_depth(child))
return np.max(depths)+1
if __name__ == '__main__':
""" Let us create following example tree
50
/ \
30 70
"""
root = Node(50)
root.spawn_child(30)
root.spawn_child(70)
print(max_depth(root)) # results in RecursionError
Upon checking the max_depth of the tree here we get an error. We have infact created the tree,
50
/ \
30 70
/ \ / \
30 70 30 70
/ \ / \
30 70 30 70
/ \ / \
. . . .
. . . .
. . . .
Upon removing the keyword argument children=[] and rewritting the constructor as,
class Node:
# Constructor to create a Node
def __init__(self, data):
self.value = data
self.children = []
we stop the recursive generation of child nodes and generate the correct tree i.e. one root node with a value of 50 which has two children (30 and 70). Now the correct value of max_depth() is printed as 1.
How does including the children attribute as a default keyword with a value corrosponding to an empty list cause this behaviour?
