tree_traversal.py

# python 2.7+
class Node(object):
    
    def __init__(self, value, left, right):
        self.value = value
        self.left = left
        self.right = right
    
    def __iter__(self):
        yield self.value
        for n in self.left:
            yield n
        for n in self.right:
            yield n

# python 3.3+
class Node:
    
    def __init__(self, value, left, right):
        self.value = value
        self.left = left
        self.right = right
    
    def __iter__(self):
        yield self.value
        yield from self.left
        yield from self.right
        

# fn.py
from fn import Stream

class Node:
    
    def __init__(self, value, left, right):
        self.value = value
        self.left = left
        self.right = right
    
    def __iter__(self):
        # compare to:
        # return (self.value #:: self.left #:: self.right)
        return iter(Stream(self.value) << self.left << self.right)