Generator send(), throw() & close() Coroutine Basics

1Concept

Generators can receive data from callers via `.send(value)`. Calling `.throw(Exception)` injects an exception at the yield point, and `.close()` raises `GeneratorExit` to terminate the generator safely.

2Architecture Diagram

Caller ---> .send("Data") ---> [ yield resumes with "Data" ] ---> Computes next state

3Code Example

def accumulator():
    total = 0
    while True:
        val = yield total
        if val is None:
            break
        total += val

acc = accumulator()
next(acc) # Prime the generator to first yield point
print(f"Accumulated: {acc.send(10)}")
print(f"Accumulated: {acc.send(25)}")
acc.close()
print("Accumulator coroutine closed safely.")

4Expected Output

Accumulated: 10
Accumulated: 35
Accumulator coroutine closed safely.

5Key Takeaways

• ✓Generators must be 'primed' with `next(gen)` or `gen.send(None)` before sending values.
• ✓`GeneratorExit` exception is caught inside generators to execute resource cleanup.
• ✓This generator co-routine mechanic was the historical precursor to modern `async`/`await` in Python.