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1. What does this program print, one line per print? ``

python
from dataclasses import dataclass

@dataclass(frozen=True)
class Tag:
    is_set: bool
    value: int
    add: int

    def then(self, later):
        if later.is_set:
            return later
        return Tag(self.is_set, self.value, self.add + later.add)

NONE = Tag(False, 0, 0)

print(Tag(False, 0, 9).then(Tag(True, 5, 0)))
print(Tag(True, 5, 0).then(Tag(False, 0, 2)))
print(NONE.then(Tag(False, 0, 3)))

``

Tag(is_set=False, value=0, add=9) Tag(is_set=True, value=5, add=2) Tag(is_set=False, value=0, add=3)Tag(is_set=True, value=5, add=9) Tag(is_set=True, value=5, add=2) Tag(is_set=False, value=0, add=3)Tag(is_set=True, value=5, add=0) Tag(is_set=True, value=5, add=2) Tag(is_set=False, value=0, add=3)Tag(is_set=True, value=5, add=0) Tag(is_set=True, value=5, add=0) Tag(is_set=False, value=0, add=3)

2. What does this program print, one value per line? ``

python
def apply_to_sum(old_sum, length, is_set, value, add):
    if is_set:
        return (value + add) * length
    return old_sum + add * length

print(apply_to_sum(100, 3, True, 5, 2))
print(apply_to_sum(100, 3, False, 0, 4))
print(apply_to_sum(100, 4, True, 1, 0))

``

21, 112, 421, 100, 415, 112, 421, 112, 1

3. A node has the pending tag "add 3", then receives "assign 4", then receives "add 1". Which single tag should it hold?

Tag(is_set=False, value=0, add=8)Tag(is_set=True, value=4, add=1)Tag(is_set=True, value=4, add=4)Tag(is_set=True, value=8, add=1)

4. Why does push set the node's tag back to NONE after it passes the tag down to both children?

So the children can read the node's sumSo the same change is not passed down again later and applied twiceSo an assignment can be undoneSo the node's sum is not recomputed after a change

5. After assign 5 and then add 2 on a node, the node holds one combined tag. Write it as Python code.

Type your answer.

Lazy assignments