Python：递归函数后打印新行

Question

I'm writing a tree traversal method. The output needs to be on one line. When the method is complete, though, I'd like to insert a line break. Is there any way to do this within the function, or will it have to be called from outside?

Right now I have:

def postorder_transversal(self):
    if self.node == None:
        return 0
    for child in self.children:
        child.postorder_transversal()
    print self.node,

Any thoughts on how to alter it?

Answer 1

You could do it inside the function like so:

def postorder_transversal(self, add_newline=True):
    if self.node == None:
        return 0
    for child in self.children:
        child.postorder_transversal(add_newline=False)
    print self.node,
    if add_newline:
        print

though it may be cleaner to just do it outside.

Answer 2

You could pass the depth as a parameter:

def postorder_transversal(self, depth=0):
    if self.node == None:
        return 0

    for child in self.children:
        child.postorder_transversal(depth=depth + 1)

    print self.node,

    if depth == 0:
        print

And with the print function:

from __future__ import print_function

def postorder_transversal(self, depth=0):
    if self.node == None:
        return 0

    for child in self.children:
        child.postorder_transversal(depth=depth + 1)

    print(self.node, end='\n' * (depth == 0))

Answer 3

After this function backs out of recursion, it will print a bunch of nodes. Right after that, add a newline to stdout. So yes, outside.