Using Yield as intermediate state update mechanism in python

non_blocking_state_update.py

"""
Goal: show how a generator can flush an “early” state patch
      before a slow computation finishes.
"""

import time
from copy import deepcopy


# ── 1. The “state object” we want to keep in sync ──────────────────────────
state = {"is_loading": False, "result": None}


# ── 2. A helper that mimics Reflex’s diff-and-patch emitter ────────────────
def flush(prev: dict, curr: dict):
    """Print only the keys whose values changed."""
    patch = {k: v for k, v in curr.items() if prev.get(k) != v}
    if patch:
        print("PATCH ➜", patch)


# ── 3. Slow worker (pretend this is Pandas, network, etc.) ─────────────────
def process_state(value: int) -> int:
    time.sleep(2)                    # heavy work (blocking)
    return value * value


# ── 4. The *generator* handler with a single `yield` ───────────────────────
def handle_submit(x: int):
    state["is_loading"] = True       # set busy flag
    yield                            # ✧ early flush here ✧

    state["result"] = process_state(x)

    state["is_loading"] = 'MOnkey'       # set busy flag
    yield 

    state["result"] = process_state(x*45)
    state["is_loading"] = False      # clear flag
    # (generator ends – final flush happens in driver)


# ── 5. A tiny “event loop” that drives the generator ───────────────────────
def run_handler(gen):
    prev = deepcopy(state)           # snapshot before we start
    while True:
        try:
            next(gen)
        except StopIteration:
            break
        finally:
            flush(prev, state)               # first patch (is_loading=True)
            prev = deepcopy(state)


# ── 6. Kick it off ─────────────────────────────────────────────────────────
if __name__ == "__main__":
    print("-- click --")
    run_handler(handle_submit(7))