【问题标题】：How to make Django 3, channels and uvicorn work together如何让 Django 3、channels 和 uvicorn 一起工作
【发布时间】：2020-10-11 16:06:01
【问题描述】：

我一直在尝试从 daphne 切换到 uvicorn 用于使用 django 3 和频道的项目进行生产。我在为频道加载经典 asgi 文件时遇到了错误。由于对 django.setup 或 get_application 的同步调用，我无法使用它。我试图用 sync_to_async 调用调整这个文件，但没有成功。有没有人设法让它工作？

原始 asgi.py

代码

import os
import django
from channels.routing import get_default_application


os.environ.setdefault("DJANGO_SETTINGS_MODULE", "config.settings")

django.setup()
application = get_default_application()

堆栈跟踪

Traceback (most recent call last):                                                                                                                                              
File "/usr/local/lib/python3.8/multiprocessing/process.py", line 315, in _bootstrap                                                                                           
  self.run()                                                                                                                                                                  
File "/usr/local/lib/python3.8/multiprocessing/process.py", line 108, in run                                                                                                  
  self._target(*self._args, **self._kwargs)                                                                                                                                   
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/uvicorn/subprocess.py", line 61, in subprocess_started                           
  target(sockets=sockets)                                                                                                                                                     
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/uvicorn/main.py", line 407, in run                                               
  loop.run_until_complete(self.serve(sockets=sockets))                                                                                                                        
File "/usr/local/lib/python3.8/asyncio/base_events.py", line 612, in run_until_complete                                                                                       
  return future.result()                                                                                                                                                      
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/uvicorn/main.py", line 414, in serve                                             
  config.load()                                                                                                                                                               
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/uvicorn/config.py", line 300, in load                                            
  self.loaded_app = import_from_string(self.app)                                                                                                                              
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/uvicorn/importer.py", line 20, in import_from_string                             
  module = importlib.import_module(module_str)                                                                                                                                
File "/usr/local/lib/python3.8/importlib/__init__.py", line 127, in import_module                                                                                             
  return _bootstrap._gcd_import(name[level:], package, level)                                                                                                                 
File "<frozen importlib._bootstrap>", line 1014, in _gcd_import                                                                                                               
File "<frozen importlib._bootstrap>", line 991, in _find_and_load                                                                                                             
File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked                                                                                                    
File "<frozen importlib._bootstrap>", line 671, in _load_unlocked                                                                                                             
File "<frozen importlib._bootstrap_external>", line 783, in exec_module                                                                                                       
File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed                                                                                                  
File "./config/asgi.py", line 16, in <module>                                                                                                                                 
  django.setup()                                                                                                                                                              
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/__init__.py", line 24, in setup                                           
  apps.populate(settings.INSTALLED_APPS)                                                                                                                                      
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/apps/registry.py", line 122, in populate                                  
  app_config.ready()                                                                                                                                                          
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django_prometheus/apps.py", line 23, in ready                                    
  ExportMigrations()                                                                                                                                                          
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django_prometheus/migrations.py", line 52, in ExportMigrations                   
  executor = MigrationExecutor(connections[alias])                                                                                                                            
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/db/migrations/executor.py", line 18, in __init__                          
  self.loader = MigrationLoader(self.connection)                                                                                                                              
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/db/migrations/loader.py", line 49, in __init__                            
  self.build_graph()                                                                                                                                                          
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/db/migrations/loader.py", line 212, in build_graph                        
  self.applied_migrations = recorder.applied_migrations()                                                                                                                     
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/db/migrations/recorder.py", line 76, in applied_migrations                
  if self.has_table():                                                                                                                                                        
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/db/migrations/recorder.py", line 56, in has_table                         
  return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())                                                                 
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/django/utils/asyncio.py", line 24, in inner
  raise SynchronousOnlyOperation(message)
django.core.exceptions.SynchronousOnlyOperation: You cannot call this from an async context - use a thread or sync_to_async.

修改 asgi.py

代码

import os
import django
from asgiref.sync import sync_to_async
from channels.routing import get_default_application


os.environ.setdefault("DJANGO_SETTINGS_MODULE", "config.settings")
sync_to_async(django.setup, thread_sensitive=True)
application = sync_to_async(get_default_application, thread_sensitive=True)

堆栈跟踪

Traceback (most recent call last):
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/uvicorn/lifespan/on.py", line 55, in main
  await app(scope, self.receive, self.send)
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
  return await self.app(scope, receive, send)
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/asgiref/sync.py", line 296, in __call__
  ret = await asyncio.wait_for(future, timeout=None)
File "/usr/local/lib/python3.8/asyncio/tasks.py", line 455, in wait_for
  return await fut
File "/usr/local/lib/python3.8/concurrent/futures/thread.py", line 57, in run
  result = self.fn(*self.args, **self.kwargs)
File "/var/www/.cache/pypoetry/virtualenvs/project-4ffvdAoS-py3.8/lib/python3.8/site-packages/asgiref/sync.py", line 334, in thread_handler
  return func(*args, **kwargs)
TypeError: get_default_application() takes 0 positional arguments but 3 were given
ERROR:    Application startup failed. Exiting.

感谢大家阅读我的文章

【问题讨论】：

嘿@Eclar，我实际上遇到了和你一样的问题。我了解正确答案中的内容，但我在实施时遇到了麻烦。我正在使用 Docker（和 Django-Cookie-Cutter 框架），但我似乎无法正确执行此操作。我的 asgi.py 文件中有 uvicorn.run，但是当从 bash 脚本调用 asgi.py 脚本时，它总是告诉我 django no module name 'config'。想知道你是否遇到过这个。

标签： django django-channels django-3.0 uvicorn

【解决方案1】：

您传递给 uvicorn 的可调用对象将按照 function 在事件循环中运行
由于1.django.setup()需要转为协程
get_default_application() 不应该异步运行，它会自动神奇地返回路由器应用程序。这就是 uvicorn 应该指向的地方。
django.setup() 必须在主事件循环开始之前返回

鉴于这四点，您的代码应该如下：

import os
import django
from asgiref.sync import sync_to_async
from channels.routing import get_default_application


os.environ.setdefault("DJANGO_SETTINGS_MODULE", "config.settings")
await sync_to_async(django.setup, thread_sensitive=True)()
application = get_default_application()

但是，在撰写本文时，您不能将 await 用作顶级指令，并且如果您将其删除，则无法保证在解析模块之前完成设置（它不会）。因此，如果您在启动应用程序之前要运行同步代码，则不能使用 uvicorn 的命令行。

但是，您可以通过编程方式启动它：


# server.py

import uvicorn
import os
import django

from channels.routing import get_default_application


os.environ.setdefault("DJANGO_SETTINGS_MODULE", "config.settings")
django.setup()

app = get_default_application()

    
if __name__ == "__main__":
    uvicorn.run("server:app") # Pass additional command line options as kwargs

【讨论】：