Print root and children in a tree in python

Question

I have a program that creates a tree by nesting the object creation as below. I know its not the correct way but I have to print the values at each level.

class Node(object):
    def __init__(self, value, children):
        self.value = value
        self.children = children


exTree = Node(1, [
              Node(2, []), Node(3, [
                   Node(4, [
                        Node(5, []), Node(6, [
                             Node(7,[])
              ])])])])

I tried accessing the values but couldn't find a way.

The tree is as below -

And I have to print the values as below:

print(treeToString(extree)
>1
>23
>4
>56
>7  

UPDATE - I am able to achieve the following so far but its not in the correct format required. I have to create one function only.

def treeToString(exTree):
    print(exTree.value)
    for child in exTree.children:
        treeToString(child)

treeToString(extree)

Output -

1
2
3
4
5
6
7

Answer 1

I have solved it in the following way:

def treeToString(extree):
   rep = str(extree.value) + "\n"
   return _treeToStringAux(extree, rep)

def _treeToStringAux(extree, rep):
    for child in extree.children:
        rep+= str(child.value)
    if not (rep[-1] == "\n"):
        rep+="\n"
    for child in extree.children:
        rep = _treeToStringAux(child, rep)
    return rep


print(treeToString(exTree)) 

gives the result.

The part where I check the \n is because due to the way I traverse the tree I sometimes get two newlines

Answer 2

I would use a generator to yield one level at a time. This is very versatile as it lets you do all kinds of things with the output, not just print .

def levels(trees):
    if trees:
        yield tuple([tree.value for tree in trees])
        yield from levels([child for tree in trees for child in tree.children])

Example:

>>> list(levels([exTree]))
[(1,), (2, 3), (4,), (5, 6), (7,)]

From there, you can print if you like, or write pytests and doctests, or use in other applications.

for v in levels([exTree]):
    print(' '.join(map(str, v)))

Output:

1
2 3
4
5 6
7

(Note: use ''.join(...) above to suppress the space and match exactly your desired output, but I think it's more explanatory with the space).