理解Flask上下文环境

flask_context.py

import flask
from flask import Flask

app = Flask(__name__)


@app.route("/")
def index():
    return "hello"


@app.before_request
def before_request():
    print("before_request")


@app.teardown_request
def teardown_request(ex):
    print("teardown_request")


@app.teardown_appcontext
def teardown_appcontext(ex):
    print("teardown_appcontext")


@flask.appcontext_pushed.connect_via(app)
def appcontext_pushed(sender, *args, **kwargs):
    print("appcontext_pushed")


@flask.appcontext_popped.connect_via(app)
def appcontext_popped(sender, *args, **kwargs):
    print("appcontext_popped")


@flask.appcontext_tearing_down.connect_via(app)
def appcontext_tearing_down(sender, *args, **kwargs):
    print("appcontext_tearing_down")


@flask.request_tearing_down.connect_via(app)
def request_tearing_down(sender, *args, **kwargs):
    print("request_tearing_down")


@flask.request_finished.connect_via(app)
def request_finished(sender, *args, **kwargs):
    print("request_finished")


@flask.request_started.connect_via(app)
def request_started(sender, *args, **kwargs):
    print("request_started")

if __name__ == '__main__':
    with app.app_context():
        print("-" * 60)
        with app.test_client() as c:
            c.get("/")
        print("-" * 40)
        with app.test_client() as c:
            c.get("/")
        print("-" * 60)
    print("-" * 40)
    with app.test_client() as c:
        c.get("/")
    print("-" * 40)
    with app.test_client() as c:
        c.get("/")
    app.run()

output.txt

appcontext_pushed
------------------------------------------------------------
request_started
before_request
request_finished
teardown_request
request_tearing_down
----------------------------------------
request_started
before_request
request_finished
teardown_request
request_tearing_down
------------------------------------------------------------
teardown_appcontext
appcontext_tearing_down
appcontext_popped
----------------------------------------
appcontext_pushed
request_started
before_request
request_finished
teardown_request
request_tearing_down
teardown_appcontext
appcontext_tearing_down
appcontext_popped
----------------------------------------
appcontext_pushed
request_started
before_request
request_finished
teardown_request
request_tearing_down
teardown_appcontext
appcontext_tearing_down
appcontext_popped
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
appcontext_pushed
request_started
before_request
request_finished
teardown_request
request_tearing_down
teardown_appcontext
appcontext_tearing_down
appcontext_popped
127.0.0.1 - - [11/Oct/2016 16:32:55] "GET / HTTP/1.1" 200 -

请求上下文与应用上下文是一一对应的。
在手动推入应用上下文的情况下，一个应用上下文对应多个请求上下文，
这是异常情况，一般会在测试的时候出现，需要避免这样的写法。