适用于 Python 3 的延迟 API

本页面介绍如何将 Deferred API（一种旧版捆绑服务）与标准环境中的 Python 3 运行时搭配使用。您的应用可以通过 Python 3 版 App Engine 服务 SDK 访问捆绑服务。

概览

延迟软件包 google.appengine.ext.deferred 过去依赖于 Python 2 中的 webapp 框架。由于 Python 3 版 App Engine 服务 SDK 中已移除 webapp 框架，因此在将 Python 2 应用升级到 Python 3 时，您需要做出一些更改。

启用 Deferred API

要为 Python 3 启用 Deferred API，您不再需要在 app.yaml 文件中将 builtins.deferred 设置为 on。如需启用 API，您必须在对 wrap_wsgi_app() 的调用中传递 use_deferred=True。

相似之处和不同之处

默认情况下，适用于 Python 3 的 Deferred API 使用与 Python 2 中相同的网址 /_ah/queue/deferred 和默认队列。请注意，对于迁移到 Cloud Tasks 的应用，系统不会自动创建默认队列，并且延迟任务库不可用。

如果您的应用使用默认的 /_ah/queue/deferred 端点，则使用 Python 3 中的 deferred.defer() 与使用 Python 2 的效果相同。如果您的应用使用自定义网址来执行延迟任务，则需要进行一些更改，因为 Python 2 的 deferred 模块中的 TaskHandler 类已从此 API 的 Python 3 版本中移除了。

如需为执行延迟任务设置自定义网址，应用可替换 deferred.Handler 类中的 post 或 run_from_request 方法（先前在 Python 2 中称为 deferred.TaskHandler），并传递 environ 参数，该参数表示包含 WSGI 请求参数的字典。然后，可以从自定义端点调用 post 方法（如 Python 3 示例所示）。

Python 3 Deferred API 的端到端使用情况（例如请求路由和访问 environ 字典）取决于应用要迁移到的 Web 框架。比较以下几个部分中 Python 2 示例与 Python 3 示例的代码更改。

Python 3 示例

以下示例展示了如何在 Flask 应用和 Django 应用中使用默认端点和自定义端点执行延迟任务。

Flask

import os

from flask import Flask, request
from google.appengine.api import wrap_wsgi_app
from google.appengine.ext import deferred
from google.appengine.ext import ndb

my_key = os.environ.get("GAE_VERSION", "Missing")

app = Flask(__name__)
app.wsgi_app = wrap_wsgi_app(app.wsgi_app, use_deferred=True)

class Counter(ndb.Model):
    count = ndb.IntegerProperty(indexed=False)

def do_something_later(key, amount):
    entity = Counter.get_or_insert(key, count=0)
    entity.count += amount
    entity.put()

@app.route("/counter/increment")
def increment_counter():
    # Use default URL and queue name, no task name, execute ASAP.
    deferred.defer(do_something_later, my_key, 10)

    # Use default URL and queue name, no task name, execute after 1 minute.
    deferred.defer(do_something_later, my_key, 10, _countdown=60)

    # Providing non-default task queue arguments
    deferred.defer(do_something_later, my_key, 10, _url="/custom/path", _countdown=120)

    return "Deferred counter increment."

@app.route("/counter/get")
def view_counter():
    counter = Counter.get_or_insert(my_key, count=0)
    return str(counter.count)

@app.route("/custom/path", methods=["POST"])
def custom_deferred():
    print("Executing deferred task.")
    # request.environ contains the WSGI `environ` dictionary (See PEP 0333)
    return deferred.Handler().post(request.environ)

Django

import os

from django.conf import settings
from django.core.wsgi import get_wsgi_application
from django.http import HttpResponse
from django.urls import path
from google.appengine.api import wrap_wsgi_app
from google.appengine.ext import deferred
from google.appengine.ext import ndb

my_key = os.environ.get("GAE_VERSION", "Missing")

class Counter(ndb.Model):
    count = ndb.IntegerProperty(indexed=False)

def do_something_later(key, amount):
    entity = Counter.get_or_insert(key, count=0)
    entity.count += amount
    entity.put()

def increment_counter(request):
    # Use default URL and queue name, no task name, execute ASAP.
    deferred.defer(do_something_later, my_key, 10)

    # Use default URL and queue name, no task name, execute after 1 minute.
    deferred.defer(do_something_later, my_key, 10, _countdown=60)

    # Providing non-default task queue arguments
    deferred.defer(do_something_later, my_key, 10, _url="/custom/path", _countdown=120)

    return HttpResponse("Deferred counter increment.")

def view_counter(request):
    counter = Counter.get_or_insert(my_key, count=0)
    return HttpResponse(str(counter.count))

def custom_deferred(request):
    print("Executing deferred task.")
    # request.environ contains the WSGI `environ` dictionary (See PEP 0333)
    response, status, headers = deferred.Handler().post(request.environ)
    return HttpResponse(response, status=status.value)

urlpatterns = (
    path("counter/get", view_counter, name="view_counter"),
    path("counter/increment", increment_counter, name="increment_counter"),
    path("custom/path", custom_deferred, name="custom_deferred"),
)

settings.configure(
    DEBUG=True,
    SECRET_KEY="thisisthesecretkey",
    ROOT_URLCONF=__name__,
    MIDDLEWARE_CLASSES=(
        "django.middleware.common.CommonMiddleware",
        "django.middleware.csrf.CsrfViewMiddleware",
        "django.middleware.clickjacking.XFrameOptionsMiddleware",
    ),
    ALLOWED_HOSTS=["*"],
)

app = wrap_wsgi_app(get_wsgi_application(), use_deferred=True)

没有任何框架

import os
import re

from google.appengine.api import wrap_wsgi_app
from google.appengine.ext import deferred
from google.appengine.ext import ndb

my_key = os.environ.get("GAE_VERSION", "Missing")

class Counter(ndb.Model):
    count = ndb.IntegerProperty(indexed=False)

def do_something_later(key, amount):
    entity = Counter.get_or_insert(key, count=0)
    entity.count += amount
    entity.put()

def IncrementCounter(environ, start_response):
    # Use default URL and queue name, no task name, execute ASAP.
    deferred.defer(do_something_later, my_key, 10)

    # Use default URL and queue name, no task name, execute after 1 minute.
    deferred.defer(do_something_later, my_key, 10, _countdown=60)

    # Providing non-default task queue arguments
    deferred.defer(do_something_later, my_key, 10, _url="/custom/path", _countdown=120)

    start_response("200 OK", [("Content-Type", "text/html")])
    return [b"Deferred counter increment."]

def ViewCounter(environ, start_response):
    counter = Counter.get_or_insert(my_key, count=0)
    start_response("200 OK", [("Content-Type", "text/html")])
    return [str(counter.count).encode("utf-8")]

class CustomDeferredHandler(deferred.Handler):
    """Deferred task handler that adds additional logic."""

    def post(self, environ):
        print("Executing deferred task.")
        return super().post(environ)

routes = {
    "counter/increment": IncrementCounter,
    "counter/get": ViewCounter,
    "custom/path": CustomDeferredHandler(),
}

class WSGIApplication:
    def __call__(self, environ, start_response):
        path = environ.get("PATH_INFO", "").lstrip("/")
        for regex, handler in routes.items():
            match = re.search(regex, path)
            if match is not None:
                return handler(environ, start_response)

        start_response("404 Not Found", [("Content-Type", "text/plain")])
        return [b"Not found"]

app = wrap_wsgi_app(WSGIApplication(), use_deferred=True)

代码示例

如需查看本指南中的完整代码示例，请参阅 GitHub。