I want to return a list of the values from the binary tree. Is there a shorter and more efficient way to write the method for numbers?
class BTNode(object): """A node in a binary tree.""" def __init__(self, item, left=None, right=None): """(BTNode, object, BTNode, BTNode) -> NoneType Initialize this node to store item and have children left and right, as well as depth 0. """ self.item = item self.left = left self.right = right self.depth = 0 # the depth of this node in a tree def number(self: 'BTNode') -> list: lst =  if self.right is None and self.left is None: lst.append(self.item) else: lst.append(self.item) if self.left: left = self.left.number() lst.extend(left) if self.right: right = self.right.number() lst.extend(right) return lst