Django 3.1中的异步视图

编写异步代码能够毫不费力地加速应用程序。随着Django 3.1最终支持异步视图，中间件和测试，现在是将它们置入现实的好时机。

这篇文章探讨了如何开始使用Django的新异步视图。

如果想了解有关异步代码背后的强大功能以及Python中线程，多处理和异步之间的区别的更多信息，请查看我的《通过并发，并行和异步编写Speeding Up Python》。

目标
在这篇文章的结尾，您应该能够：

在Django中编写异步视图
在Django视图中发出非阻塞HTTP请求
使用Django的异步视图简化基本的后台任务
使用sync_to_async在异步视图内进行同步调用
说明何时应该和不应该使用异步视图
您还应该能够回答以下问题：

如果您在异步视图中进行同步调用怎么办？
如果您在异步视图中进行同步和异步调用怎么办？
Celery是否仍然需要Django的异步视图？

先决条件
只要您已经熟悉Django本身，向非基于类的视图添加异步功能就非常简单。

依存关系
Python> = 3.8
Django> = 3.1
葡萄胎
HTTPX

什么是ASGI？
ASGI代表异步服务器网关接口。它是WSGI的现代，异步的后续产品，为创建基于Python的异步Web应用程序提供了标准。

值得一提的另一件事是，ASGI与WSGI向后兼容，即使您不准备转向编写异步应用程序，也可以将其从Gunicorn或uWSGI之类的WSGI服务器切换至Uvicorn或Daphne之类的ASGI服务器。。

创建应用
创建一个新的项目目录以及一个新的Django项目：

$ mkdir django-async-views && cd django-async-views
$ python3.8 -m venv env
$ source env/bin/activate

(env)$ pip install django
(env)$ django-admin.py startproject hello_async .

$ mkdir django-async-views && cd django-async-views

$ python3.8 -m venv env

$ source env/bin/activate

(env)$ pip install django

(env)$ django-admin.py startproject hello_async .

如果使用内置开发服务器，则Django将运行您的异步视图，但实际上不会异步运行它们，因此我们将使用Uvicorn来支撑服务器。

安装它：

(env)$ pip install uvicorn

1	(env)$ pip install uvicorn

要使用Uvicorn运行项目，请从项目的根目录使用以下命令：

uvicorn {name of your project}.asgi:application

1	uvicorn {name of your project}.asgi:application

我们的例子：

(env)$ uvicorn hello_async.asgi:application

1	(env)$ uvicorn hello_async.asgi:application

接下来，让我们创建第一个异步视图。添加一个新文件以将视图保存在“ hello_async”文件夹中，然后添加以下视图：

# hello_async/views.py

from django.http import HttpResponse


async def index(request):
    return HttpResponse("Hello, async Django!")

# hello_async/views.py

from django.http import HttpResponse

async def index(request):

return HttpResponse("Hello, async Django!")

在Django中创建异步视图就像创建同步视图一样简单-您所需要做的就是添加async关键字。

更新网址：

# hello_async/urls.py

from django.contrib import admin
from django.urls import path

from hello_async.views import index


urlpatterns = [
    path("admin/", admin.site.urls),
    path("", index),
]

# hello_async/urls.py

from django.contrib import admin

from django.urls import path

from hello_async.views import index

urlpatterns = [

path("admin/", admin.site.urls),

path("", index),

]

终端运行：

(env)$ uvicorn hello_async.asgi:application --reload

1	(env)$ uvicorn hello_async.asgi:application --reload

–reload标志告诉uvicorn监视文件中的更改，如果发现更改，则重新加载。那可能是不言而喻的。

打开http://127.0.0.1:8000 显示：

Hello, async Django!

1	Hello, async Django!

这不是世界上最令人兴奋的事情，但是，嘿，这是一个开始。值得注意的是，使用Django的内置开发服务器运行此视图将获得完全相同的功能和输出。这是因为我们实际上没有在处理程序中执行任何异步操作。

HTTPX
值得注意的是，异步支持是完全向后兼容的，因此可以混合使用异步和同步视图，中间件和测试。 Django将在适当的执行上下文中执行每个。

为了说明这一点，请添加一些新视图：

# hello_async/views.py

import asyncio
from time import sleep

import httpx
from django.http import HttpResponse


# helpers

async def http_call_async():
    for num in range(1, 6):
        await asyncio.sleep(1)
        print(num)
    async with httpx.AsyncClient() as client:
        r = await client.get("https://httpbin.org/")
        print(r)


def http_call_sync():
    for num in range(1, 6):
        sleep(1)
        print(num)
    r = httpx.get("https://httpbin.org/")
    print(r)


# views

async def index(request):
    return HttpResponse("Hello, async Django!")


async def async_view(request):
    loop = asyncio.get_event_loop()
    loop.create_task(http_call_async())
    return HttpResponse("Non-blocking HTTP request")


def sync_view(request):
    http_call_sync()
    return HttpResponse("Blocking HTTP request")

# hello_async/views.py

import asyncio

from time import sleep

import httpx

from django.http import HttpResponse

# helpers

async def http_call_async():

for num in range(1, 6):

await asyncio.sleep(1)

print(num)

async with httpx.AsyncClient() as client:

r = await client.get("https://httpbin.org/")

print(r)

def http_call_sync():

for num in range(1, 6):

sleep(1)

print(num)

r = httpx.get("https://httpbin.org/")

print(r)

# views

async def index(request):

return HttpResponse("Hello, async Django!")

async def async_view(request):

loop = asyncio.get_event_loop()

loop.create_task(http_call_async())

return HttpResponse("Non-blocking HTTP request")

def sync_view(request):

http_call_sync()

return HttpResponse("Blocking HTTP request")

更新urls.py文件：

# hello_async/urls.py

from django.contrib import admin
from django.urls import path

from hello_async.views import index, async_view, sync_view


urlpatterns = [
    path("admin/", admin.site.urls),
    path("async/", async_view),
    path("sync/", sync_view),
    path("", index),
]

# hello_async/urls.py

from django.contrib import admin

from django.urls import path

from hello_async.views import index, async_view, sync_view

urlpatterns = [

path("admin/", admin.site.urls),

path("async/", async_view),

path("sync/", sync_view),

path("", index),

]

安装HTTPX:

(env)$ pip install httpx

1	(env)$ pip install httpx

在服务器运行的情况下，导航到http：// localhost：8000 / async /。应该立即看到响应：

Non-blocking HTTP request

1	Non-blocking HTTP request

在终端可以看到如下：

INFO:     127.0.0.1:60374 - "GET /async/ HTTP/1.1" 200 OK
1
2
3
4
5
<Response [200 OK]>

INFO: 127.0.0.1:60374 - "GET /async/ HTTP/1.1" 200 OK

在这里，HTTP响应在第一个睡眠调用之前发回。

接下来，浏览至http：// localhost：8000 / sync /。得到响应大约需要五秒钟：

Blocking HTTP request

1	Blocking HTTP request

终端显示：

1
2
3
4
5
<Response [200 OK]>
INFO:     127.0.0.1:60375 - "GET /sync/ HTTP/1.1" 200 OK

INFO: 127.0.0.1:60375 - "GET /sync/ HTTP/1.1" 200 OK

在此，HTTP响应在循环后发送，并且对https://httpbin.org/的请求完成。

抽一些肉
现在，让我们编写一个在后台运行简单任务的视图。

返回项目的URLconf，在smoke_some_meats创建一个新路径：

# hello_async/urls.py

from django.contrib import admin
from django.urls import path

from hello_async.views import index, async_view, sync_view, smoke_some_meats


urlpatterns = [
    path("admin/", admin.site.urls),
    path("smoke_some_meats/", smoke_some_meats),
    path("async/", async_view),
    path("sync/", sync_view),
    path("", index),
]

# hello_async/urls.py

from django.contrib import admin

from django.urls import path

from hello_async.views import index, async_view, sync_view, smoke_some_meats

urlpatterns = [

path("admin/", admin.site.urls),

path("smoke_some_meats/", smoke_some_meats),

path("async/", async_view),

path("sync/", sync_view),

path("", index),

]

返回的视图，创建一个新的异步函数，称为Smoke。该函数有两个参数：一个名为smokables的字符串列表和一个名为flavour的字符串。这些将分别默认为可吸烟的肉和“甜宝贝雷的”的列表。

# hello_async/views.py

async def smoke(smokables: List[str] = None, flavor: str = "Sweet Baby Ray's") -> None:
    """ Smokes some meats and applies the Sweet Baby Ray's """

    if smokables is None:
        smokables = [
            "ribs",
            "brisket",
            "lemon chicken",
            "salmon",
            "bison sirloin",
            "sausage",
        ]

    if (loved_smokable := smokables[0]) == "ribs":
        loved_smokable = "meats"

    for smokable in smokables:
        print(f"Smoking some {smokable}....")
        await asyncio.sleep(1)
        print(f"Applying the {flavor}....")
        await asyncio.sleep(1)
        print(f"{smokable.capitalize()} smoked.")

    print(f"Who doesn't love smoked {loved_smokable}?")

# hello_async/views.py

async def smoke(smokables: List[str] = None, flavor: str = "Sweet Baby Ray's") -> None:

""" Smokes some meats and applies the Sweet Baby Ray's """

if smokables is None:

smokables = [

"ribs",

"brisket",

"lemon chicken",

"salmon",

"bison sirloin",

"sausage",

]

if (loved_smokable := smokables[0]) == "ribs":

loved_smokable = "meats"

for smokable in smokables:

print(f"Smoking some {smokable}....")

await asyncio.sleep(1)

print(f"Applying the {flavor}....")

await asyncio.sleep(1)

print(f"{smokable.capitalize()} smoked.")

print(f"Who doesn't love smoked {loved_smokable}?")

如果未提供可吸烟的功能，该函数的第一行将实例化默认的肉类列表。然后，第二个“ if”语句为可吸烟对象中的第一个对象设置一个名为loved_smokable的变量，只要第一个对象不是“肋骨”即可。 for循环将味道（读取：Sweet Baby Ray’s）异步应用于可抽烟（读取：烟熏肉）。

不要忘记导入：

from typing import List

1	from typing import List

List用于额外的键入功能。这不是必需的，可以轻松省略（只需在“ smokables”参数声明后的：List [str]旁边）。

接下来，创建使用异步烟雾功能的异步视图：

# hello_async/views.py

async def smoke_some_meats(request) -> HttpResponse:
    loop = asyncio.get_event_loop()
    smoke_args = []

    if to_smoke := request.GET.get("to_smoke"):
        # Grab smokables
        to_smoke = to_smoke.split(",")
        smoke_args += [[smokable.lower().strip() for smokable in to_smoke]]

        # Do some string prettification
        if (smoke_list_len := len(to_smoke)) == 2:
            to_smoke = " and ".join(to_smoke)
        elif smoke_list_len > 2:
            to_smoke[-1] = f"and {to_smoke[-1]}"
            to_smoke = ", ".join(to_smoke)

    else:
        to_smoke = "meats"

    if flavor := request.GET.get("flavor"):
        smoke_args.append(flavor)

    loop.create_task(smoke(*smoke_args))

    return HttpResponse(f"Smoking some {to_smoke}....")

# hello_async/views.py

async def smoke_some_meats(request) -> HttpResponse:

loop = asyncio.get_event_loop()

smoke_args = []

if to_smoke := request.GET.get("to_smoke"):

# Grab smokables

to_smoke = to_smoke.split(",")

smoke_args += [[smokable.lower().strip() for smokable in to_smoke]]

# Do some string prettification

if (smoke_list_len := len(to_smoke)) == 2:

to_smoke = " and ".join(to_smoke)

elif smoke_list_len > 2:

to_smoke[-1] = f"and {to_smoke[-1]}"

to_smoke = ", ".join(to_smoke)

else:

to_smoke = "meats"

if flavor := request.GET.get("flavor"):

smoke_args.append(flavor)

loop.create_task(smoke(*smoke_args))

return HttpResponse(f"Smoking some {to_smoke}....")

该视图将可选的查询参数设为to_smoke和flavor。 to_smoke是用逗号分隔的要吸烟的列表，而味道则是您要对其应用的内容。

该视图要做的第一件事（在标准同步视图中无法完成）是使用asyncio.get_event_loop（）抢占事件循环。然后，它分析查询参数（如果适用）（并对最终的打印语句进行一些字符串清除）。如果我们不传递任何烟雾，则to_smoke默认为“肉”。最后，返回响应以使用户知道他们正在准备美味的烧烤餐。

大。保存文件，然后返回浏览器并导航到http：// localhost：8000 / smoke_some_meats /。您应该得到以下答复：

Smoking some meats....

1	Smoking some meats....

在控制端显示：

Smoking some ribs....
INFO:     127.0.0.1:56239 - "GET /smoke_some_meats/ HTTP/1.1" 200 OK

Applying the Sweet Baby Ray's....
Ribs smoked.
Smoking some brisket....
Applying the Sweet Baby Ray's....
Brisket smoked.
Smoking some lemon chicken....
Applying the Sweet Baby Ray's....
Lemon chicken smoked.
Smoking some salmon....
Applying the Sweet Baby Ray's....
Salmon smoked.
Smoking some bison sirloin....
Applying the Sweet Baby Ray's....
Bison sirloin smoked.
Smoking some sausage....
Applying the Sweet Baby Ray's....
Sausage smoked.
Who doesn't love smoked meats?

Smoking some ribs....

INFO: 127.0.0.1:56239 - "GET /smoke_some_meats/ HTTP/1.1" 200 OK