Python: Print a list with an indentation for each sublist-CodePudding

Newbie here, I am struggling with a homework question. We are supposed to write a function that prints out a "tree". This tree contains labels, branches and trees. A tree is constructed in the following way:

example_tree = tree(1, [tree(2), tree(3, [tree(4), tree(5)]), tree(6, [tree(7)])])

The tree-function is already defined. It creates a label and can optionally contain a new sublist (the "branches").

Now we are given the following task:

"""Print a representation of this tree in which each node is
    indented by two spaces times its depth from the root.
>>> print_tree(tree(1))
1
>>> print_tree(tree(1, [tree(2)]))
1
  2
>>> numbers = tree(1, [tree(2), tree(3, [tree(4), tree(5)]), tree(6, [tree(7)])])
>>> print_tree(numbers)
1
  2
  3
    4
    5
  6
    7
"""

Our first intuition was to build the following function:

def print_tree(t, indent=0):
  for i in t:
    if len(t) > 1:
      print(i)
      indent = indent   1
    else:
      print(i)

This results in the following:

1
[2]
[3, [4], [5]]
[6, [7]]

Might someone give a pointer on how we arrive at the correct result? How to work with the indent for example? The coding is done on Google Colab.

Thanks a lot!

CodePudding user response：

This sort of task (processing tree-like structure) is most commonly done by using recursion - each branch is essentialy a tree on its own, so you treat it in the same way.

class Tree:
    def __init__(self, label, branches = None):
        if not branches:
            branches = []
        self.label = label
        self.branches = branches
    def printTree(self, depth = 0):
        print("  " * depth   str(self.label))
        for branch in self.branches:
            branch.printTree(depth 1)

numbers = Tree(1, [Tree(2), Tree(3, [Tree(4), Tree(5)]), Tree(6, [Tree(7)])])
numbers.printTree()

Output: