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binary_tree_traversals.py: Simplify with dataclasses #4336

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Apr 26, 2021
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binary_tree_traversals.py: Simplify with dataclasses #4336

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binary_tree_traversals.py: Simplify with dataclasses
cclauss Apr 17, 2021
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Update data_structures/binary_tree/binary_tree_traversals.py
cclauss Apr 21, 2021
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Optional["Node"]
cclauss Apr 22, 2021
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22 changes: 7 additions & 15 deletions data_structures/binary_tree/binary_tree_traversals.py
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Original file line number Diff line number Diff line change
@@ -1,24 +1,16 @@
# https://en.wikipedia.org/wiki/Tree_traversal
from dataclasses import dataclass


class Node:
"""
A Node has data variable and pointers to its left and right nodes.
"""

def __init__(self, data):
self.left = None
self.right = None
self.data = data
@dataclass
class Node(object):
data: int
left: "Node" = None
right: "Node" = None
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I did not notice this the first time but shouldn't this be Optional["Node"]?

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My sense was that if neither Python nor mypy was complaining about it then I would not either. This would be the only location where we would set these values to None unless we started deleting Nodes which I assumed we were not gonna do.

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@dhruvmanila dhruvmanila Apr 21, 2021 •
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Python is never going to complain as it simply does not care about type hints. mypy will complain when you run it in a bit stricter modes. Plain mypy will not complain about a lot of stuff as that's how gradual typing goes.

And no, as per this definition, the leaves of the trees (the last nodes) will have its left and right node None as there are no left and right child (we have reached the end).

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@cclauss cclauss Apr 21, 2021 •
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This would be the only location where we would set these values to None

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Yes, but that still won't allow the file to be type checked later on. The variable's correct type is Optional["Node"]. Just because it is being set None once, does not change the type of that variable. That's what 'static' means in static typing :)



def make_tree() -> Node:
root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.left.right = Node(5)
return root
return Node(1, Node(2, Node(4), Node(5)), Node(3))


def preorder(root: Node):
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