我有以下两个异步函数
from tornado.httpclient import AsyncHTTPClient
async def get_categories(): # return a list of str
# ....
http = AsyncHTTPClient()
resp = await http.fetch(....)
return [....]
async def get_details(category): # return a list of dict
# ....
http = AsyncHTTPClient()
resp = await http.fetch(....)
return [....]
现在,我需要创建一个函数来获取所有类别的详细信息(同时运行httpfetch(,并将它们组合在一起。
async def get_all_details():
categories = await get_categories()
tasks = list(map(lambda x: {'category': x, 'task':get_details(x)}, categories))
r = await asyncio.gather(*tasks) # error
# need to return [
# {'category':'aaa', 'detail':'aaa detail 1'},
# {'category':'aaa', 'detail':'aaa detail 2'},
# {'category':'bbb', 'detail':'bbb detail 1'},
# {'category':'bbb', 'detail':'bbb detail 2'},
# {'category':'bbb', 'detail':'bbb detail 3'},
# {'category':'ccc', 'detail':'ccc detail 1'},
# {'category':'ccc', 'detail':'aaa detail 2'},
# ]
但是,列表行返回错误:
类型错误:不可更改的类型:"dict">
tasks
具有以下值:
[{'category': 'aaa',
'task': <coroutine object get_docker_list at 0x000001B12B8560C0>},
{'category': 'bbb',
'task': <coroutine object get_docker_list at 0x000001B12B856F40>},
{'category': 'ccc',
'task': <coroutine object get_docker_list at 0x000001B12B856740>}]
顺便说一句,这是一种抑制http获取调用的方法吗?例如,最多有四个回迁同时运行。
gather
接受协程(或其他不可用的(参数,并以相同的顺序返回其结果的元组。您正在向它传递一系列dict,其中一些dict的值是协程。gather
不知道该怎么办,并试图将dict视为不可用对象,但很快就失败了。
生成dict列表的正确方法是只将协程传递给gather
,等待结果,并将它们处理成一个新的dict:
async def get_all_details():
category_list = await get_categories()
details_list = await asyncio.gather(
*[get_details(category) for category in category_list]
)
return [
{'category': category, 'details': details}
for (category, details) in zip(category_list, details_list)
]
BTW,这是一种抑制http获取调用的方法吗?例如,最多有四个回迁同时运行。
限制并行调用的方便而惯用的方法是使用信号量:
async def get_details(category, limit):
# acquiring the semaphore passed as `limit` will allow at most a
# fixed number of coroutines to proceed concurrently
async with limit:
... the rest of the code ...
async def get_all_details():
limit = asyncio.Semaphore(4)
category_list = await get_categories()
details_list = await asyncio.gather(
*[get_details(category, limit) for category in category_list]
)
... the rest of the code ...