Miscellaneous Notes (draft)

def Treaverse():
    # Code to be run
    ...

    Treaverse() # Entry point
    # Return point

    # The rest code to be run
    ...

while stack:

    current, status = pop()

    if status == 0:
        # Code to be run
        ...

        # Change the status of current
        push(current, 1)

        # The next function to be excuted
        push(current.next, 0)

        # Return point
        continue

    elif status == 1:
        ...

class Sentinel:
"""Unique sentinel value."""
_registry = None

def __new__(cls):
    if cls._registry is None:
        cls._registry = super().__new__(cls)
    return cls._registry

def __repr__(self):
    return 'Sentinel'

def len(self) -> int:
    return self.last + 1

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