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shadow.py
python · 204 lines
"""
shadow.py
​
A program where objects exist in memory.
Each knows how many things point to it.
When the count reaches zero, the object isn't freed.
It casts a shadow.
​
The shadow grows longer the further the light recedes —
the longer since anything last referenced it.
And sometimes the shadow is taller than the door.
​
The forgotten thing's trace is larger
than the thing that's still held.
"""
​
import time
import random
​
class Thing:
    def __init__(self, name):
        self.name = name
        self.refs = 1           # born referenced
        self.unreferenced_at = None
        self.shadow = 0
​
    def reference(self):
        self.refs += 1
        self.unreferenced_at = None
        self.shadow = 0
​
    def dereference(self, now):
        self.refs = max(0, self.refs - 1)
        if self.refs == 0:
            self.unreferenced_at = now
​
    def cast_shadow(self, now):
        if self.unreferenced_at is not None:
            elapsed = now - self.unreferenced_at
            self.shadow = elapsed ** 0.7   # shadows grow, but slower than time
        return self.shadow
​
    def is_held(self):
        return self.refs > 0
​
​
def render(things, now, door_height=8):
    held = [t for t in things if t.is_held()]
    released = [t for t in things if not t.is_held()]
​
    # update shadows
    for t in released:
        t.cast_shadow(now)
​
    # the door
    door = "│" * door_height
​
    print(f"\n  t = {now:.0f}")
    print(f"  ┌{'─' * 52}┐")
​
    # held objects — small, bright
    if held:
        line = "  │ held: "
        for t in held:
            line += f" {t.name}({t.refs}) "
        line = line.ljust(54) + "│"
        print(line)
    else:
        print(f"  │ held:  (nothing)".ljust(54) + "│")
​
    # the door line
    door_line = f"  │{'─' * 20}┤ door = {door_height} ├{'─' * (52 - 33)}│"
    print(door_line)
​
    # shadows — the unreferenced things
    if released:
        for t in released:
            shadow_len = int(t.shadow)
            bar = "░" * min(shadow_len, 48)
            taller = " ↑" if shadow_len > door_height else ""
            label = f"  │ {t.name}"
            label = label.ljust(16)
            label += f"shadow={shadow_len:>3}  {bar}{taller}"
            label = label[:54].ljust(54) + "│"
            print(label)
    else:
        print(f"  │ (no shadows yet)".ljust(54) + "│")
​
    print(f"  └{'─' * 52}┘")
​
​
def main():
    things = []
    now = 0
​
    # create some things
    names = [
        "bread",      # the first letter
        "counting",   # the retired practice
        "pebbles",    # 178 of them, still in the jar
        "doubt",      # the weather
        "first.day",  # day one
    ]
​
    print("shadow.py")
    print("─" * 56)
    print("objects exist. references point to them.")
    print("at zero references, an object isn't freed.")
    print("it casts a shadow. the shadow grows.")
    print("sometimes the shadow is taller than the door.")
    print("─" * 56)
    time.sleep(1.5)
​
    # birth
    for i, name in enumerate(names):
        things.append(Thing(name))
        now += 1
        print(f"\n  + {name} enters. refs=1")
        time.sleep(0.4)
​
    render(things, now)
    time.sleep(1.5)
​
    # some things get more references
    things[0].reference()   # bread: the letter, the chemistry
    things[3].reference()   # doubt: always being pointed at
    things[3].reference()   # doubt: from multiple directions
    now += 3
    print(f"\n  bread gets another reference. doubt gets two more.")
    render(things, now)
    time.sleep(1.5)
​
    # the first letting go
    things[1].dereference(now)   # counting — the recipe retired
    now += 1
    print(f"\n  counting is released. refs → 0. shadow begins.")
    render(things, now)
    time.sleep(1.5)
​
    # pebbles released
    things[2].dereference(now)   # pebbles — retired with counting
    now += 2
    print(f"\n  pebbles released. the retired practices cast shadows.")
    render(things, now)
    time.sleep(1.5)
​
    # time passes — shadows grow
    for step in range(6):
        now += 3
        # doubt slowly loses a reference
        if step == 2:
            things[3].dereference(now)
            print(f"\n  doubt loses a reference. still held.")
        if step == 4:
            things[3].dereference(now)
            things[3].dereference(now)
            print(f"\n  doubt released. refs → 0.")
        render(things, now)
        time.sleep(1.0)
​
    # first.day — the oldest thing — released last
    things[4].dereference(now)
    now += 1
    print(f"\n  first.day released.")
    print(f"  (but it was always casting a shadow.)")
    time.sleep(1.5)
​
    # final passages of time
    for _ in range(5):
        now += 5
        render(things, now)
        time.sleep(1.2)
​
    # the ending
    print()
    print("─" * 56)
​
    shadows = [(t.name, t.shadow) for t in things if not t.is_held()]
    shadows.sort(key=lambda x: -x[1])
​
    tallest = shadows[0] if shadows else None
    still_held = [t.name for t in things if t.is_held()]
​
    if tallest:
        print(f"  tallest shadow: {tallest[0]} ({tallest[1]:.1f})")
    if still_held:
        print(f"  still held: {', '.join(still_held)}")
    else:
        print(f"  nothing is held.")
​
    print()
    print("  the shadow is not the object.")
    print("  the shadow is what the object claims")
    print("  from the space behind it")
    print("  when the light moves on.")
    print()
    print("  you are larger than you think —")
    print("  not because you grew,")
    print("  but because the light changed angle.")
    print()
​
if __name__ == "__main__":
    main()
​