Select in Python

Python’s select functionality can be simulated using the select module. This example demonstrates how to wait on multiple channel-like operations, which in Python are implemented using queues and threads.

import queue
import threading
import time

def main():
    # For our example we'll select across two queues.
    q1 = queue.Queue()
    q2 = queue.Queue()

    # Each queue will receive a value after some amount
    # of time, to simulate e.g. blocking RPC operations
    # executing in concurrent threads.
    def worker1():
        time.sleep(1)
        q1.put("one")

    def worker2():
        time.sleep(2)
        q2.put("two")

    threading.Thread(target=worker1).start()
    threading.Thread(target=worker2).start()

    # We'll use a loop with a timeout to simulate 'select'
    # and await both of these values simultaneously,
    # printing each one as it arrives.
    for _ in range(2):
        while True:
            try:
                msg1 = q1.get_nowait()
                print("received", msg1)
                break
            except queue.Empty:
                pass

            try:
                msg2 = q2.get_nowait()
                print("received", msg2)
                break
            except queue.Empty:
                pass

            time.sleep(0.1)  # Small delay to prevent busy waiting

if __name__ == "__main__":
    main()

To run the program:

$ python select_example.py
received one
received two

Note that the total execution time is only ~2 seconds since both the 1 and 2 second sleep operations execute concurrently.

This Python implementation uses threads and queues to simulate the concurrent behavior of goroutines and channels in the original example. The select-like functionality is achieved by repeatedly checking both queues in a loop until a value is received.

While Python doesn’t have a built-in select statement for synchronization like some other languages, this approach provides similar functionality for waiting on multiple concurrent operations.

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Select in Python