下面我附上了一个测试程序来演示我遇到的asyncio.gather抛出TypeError的问题。
我的目标： 进行多个并发异步调用，以从连接到我的计算机的 USB 摄像头阵列中将摄像头图像捕获到文件中。当所有相机都完成异步捕获后，我想恢复处理。
此处显示的异步协程take_image()对“ffmpeg”应用程序进行系统调用，该应用程序将图像从指定相机捕获到指定文件。
import asyncio
import os
import subprocess
import time
async def take_image(camera_id, camera_name, image_file_path, image_counter):
image_capture_tic = time.perf_counter()
try:
run_cmd = subprocess.run( ["ffmpeg", '-y', '-hide_banner', '-f', 'avfoundation', '-i', camera_id,
'-frames:v', '1', '-f', 'image2', image_file_path], universal_newlines=True,
stdout=subprocess.PIPE, stderr=subprocess.PIPE) # Note, ffmpeg writes to stderr, not stdout!
except Exception as e:
print("Error: Unable to capture image for", image_file_path)
return "NO IMAGE!"
image_capture_toc = time.perf_counter()
print(f"{image_counter}: Captured {camera_name} image in: {image_capture_toc - image_capture_tic:0.0f} seconds")
return camera_name
下面显示的main()例程获取多个摄像头的列表，并遍历列表中的每个摄像头， main() 使用asyncio.create_task()为每个摄像头创建一个异步任务。每个任务都添加到任务列表中。
一旦所有图像捕获任务都已启动，我使用await asyncio.gather(tasks)等待它们完成。
async def main():
tic = time.perf_counter()
camera_list = [('0', 'FHD Camera #1'), ('1', 'FHD Camera #2'), ('2', 'FHD Camera #3'), ]
image_counter = 1
tasks = []
for camera_pair in camera_list:
camera_id, camera_name = camera_pair
image_file_name = 'img' + str(image_counter) + "-cam" + str(camera_id) + "-" + camera_name + '.jpg'
image_file_path = os.path.join("/tmp/test1/img", image_file_name)
# schedule all image captures calls *concurrently*:
tasks.append(asyncio.create_task(take_image(camera_id, camera_name, image_file_path, image_counter),
name=image_file_name))
image_counter = image_counter + 1
await asyncio.gather(tasks) # <-- This line throws a TypeError!
toc = time.perf_counter()
print(f"Captured list of {image_counter - 1} cameras in: {toc - tic:0.0f} seconds")
asyncio.run(main())
不幸的是，当我尝试运行这个程序时，我收到了这个错误：
类型错误：不可散列类型：“列表”
和以下追溯：
Traceback (most recent call last):
File "scratch_10.py", line 41, in <module>
asyncio.run(main())
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/asyncio/runners.py", line 43, in run
return loop.run_until_complete(main)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/asyncio/base_events.py", line 608, in run_until_complete
return future.result()
File "scratch_10.py", line 36, in main
await asyncio.gather(tasks)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/asyncio/tasks.py", line 805, in gather
if arg not in arg_to_fut:
TypeError: unhashable type: 'list'
我一直试图通过 asyncio 的 3.8 文档来解决问题，但我不明白出了什么问题。
如何让每个 take_image 请求异步运行，然后在每个任务完成后在我的调用例程中恢复处理？