flask信号

flask信号

 

Flask框架中的信号基于blinker，其主要就是让开发者可是在flask请求过程中定制一些用户行为。

pip3 install blinker

1. 内置信号

request_started = _signals.signal('request-started')                # 请求到来前执行
request_finished = _signals.signal('request-finished')              # 请求结束后执行
 
before_render_template = _signals.signal('before-render-template')  # 模板渲染前执行
template_rendered = _signals.signal('template-rendered')            # 模板渲染后执行
 
got_request_exception = _signals.signal('got-request-exception')    # 请求执行出现异常时执行
 
request_tearing_down = _signals.signal('request-tearing-down')      # 请求执行完毕后自动执行（无论成功与否）
appcontext_tearing_down = _signals.signal('appcontext-tearing-down')# 请求上下文执行完毕后自动执行（无论成功与否）
 
appcontext_pushed = _signals.signal('appcontext-pushed')            # 请求上下文push时执行
appcontext_popped = _signals.signal('appcontext-popped')            # 请求上下文pop时执行
message_flashed = _signals.signal('message-flashed')                # 调用flask在其中添加数据时，自动触发

源码示例

 

class Flask(_PackageBoundObject):

def full_dispatch_request(self):

self.try_trigger_before_first_request_functions()
try:
# ############### 触发request_started 信号 ###############
request_started.send(self)
rv = self.preprocess_request()
if rv is None:
rv = self.dispatch_request()
except Exception as e:
rv = self.handle_user_exception(e)
response = self.make_response(rv)
response = self.process_response(response)

# ############### request_finished 信号 ###############
request_finished.send(self, response=response)
return response

def wsgi_app(self, environ, start_response):

ctx = self.request_context(environ)
ctx.push()
error = None
try:
try:
response = self.full_dispatch_request()
except Exception as e:
error = e
response = self.make_response(self.handle_exception(e))
return response(environ, start_response)
finally:
if self.should_ignore_error(error):
error = None
ctx.auto_pop(error)

request_started

 

同上

 

def render_template(template_name_or_list, **context):
"""Renders a template from the template folder with the given
context.

:param template_name_or_list: the name of the template to be
rendered, or an iterable with template names
the first one existing will be rendered
:param context: the variables that should be available in the
context of the template.
"""
ctx = _app_ctx_stack.top
ctx.app.update_template_context(context)
return _render(ctx.app.jinja_env.get_or_select_template(template_name_or_list),
context, ctx.app)

def _render(template, context, app):
"""Renders the template and fires the signal"""

# ############### before_render_template 信号 ###############
before_render_template.send(app, template=template, context=context)
rv = template.render(context)

# ############### template_rendered 信号 ###############
template_rendered.send(app, template=template, context=context)
return rv

before_render_template

 

同上

 

class Flask(_PackageBoundObject):

def handle_exception(self, e):

exc_type, exc_value, tb = sys.exc_info()

# ############### got_request_exception 信号 ###############
got_request_exception.send(self, exception=e)
handler = self._find_error_handler(InternalServerError())

if self.propagate_exceptions:
# if we want to repropagate the exception, we can attempt to
# raise it with the whole traceback in case we can do that
# (the function was actually called from the except part)
# otherwise, we just raise the error again
if exc_value is e:
reraise(exc_type, exc_value, tb)
else:
raise e

self.log_exception((exc_type, exc_value, tb))
if handler is None:
return InternalServerError()
return handler(e)

def wsgi_app(self, environ, start_response):

ctx = self.request_context(environ)
ctx.push()
error = None
try:
try:
response = self.full_dispatch_request()
except Exception as e:
error = e
# 这里这里这里这里这里这里这里这里这里这里这里这里 #
response = self.make_response(self.handle_exception(e))
return response(environ, start_response)
finally:
if self.should_ignore_error(error):
error = None
ctx.auto_pop(error)

got_request_exception

 

class AppContext(object):
def push(self):
"""Binds the app context to the current context."""
self._refcnt += 1
if hasattr(sys, 'exc_clear'):
sys.exc_clear()
_app_ctx_stack.push(self)
# ############## 触发 appcontext_pushed 信号 ##############
appcontext_pushed.send(self.app)

def pop(self, exc=_sentinel):
"""Pops the app context."""
try:
self._refcnt -= 1
if self._refcnt <= 0:
if exc is _sentinel:
exc = sys.exc_info()[1]
# ############## 触发 appcontext_tearing_down 信号 ##############
self.app.do_teardown_appcontext(exc)
finally:
rv = _app_ctx_stack.pop()
assert rv is self, 'Popped wrong app context. (%r instead of %r)'
% (rv, self)

# ############## 触发 appcontext_popped 信号 ##############
appcontext_popped.send(self.app)

class RequestContext(object):
def push(self):
top = _request_ctx_stack.top
if top is not None and top.preserved:
top.pop(top._preserved_exc)

app_ctx = _app_ctx_stack.top
if app_ctx is None or app_ctx.app != self.app:

# ####################################################
app_ctx = self.app.app_context()
app_ctx.push()
self._implicit_app_ctx_stack.append(app_ctx)
else:
self._implicit_app_ctx_stack.append(None)

if hasattr(sys, 'exc_clear'):
sys.exc_clear()

_request_ctx_stack.push(self)

# Open the session at the moment that the request context is
# available. This allows a custom open_session method to use the
# request context (e.g. code that access database information
# stored on `g` instead of the appcontext).
self.session = self.app.open_session(self.request)
if self.session is None:
self.session = self.app.make_null_session()

class Flask(_PackageBoundObject):

def wsgi_app(self, environ, start_response):

ctx = self.request_context(environ)
ctx.push()
error = None
try:
try:
response = self.full_dispatch_request()
except Exception as e:
error = e
response = self.make_response(self.handle_exception(e))
return response(environ, start_response)
finally:
if self.should_ignore_error(error):
error = None
ctx.auto_pop(error)

def pop(self, exc=_sentinel):
app_ctx = self._implicit_app_ctx_stack.pop()

try:
clear_request = False
if not self._implicit_app_ctx_stack:
self.preserved = False
self._preserved_exc = None
if exc is _sentinel:
exc = sys.exc_info()[1]

# ################## 触发 request_tearing_down 信号 ##################
self.app.do_teardown_request(exc)

# If this interpreter supports clearing the exception information
# we do that now. This will only go into effect on Python 2.x,
# on 3.x it disappears automatically at the end of the exception
# stack.
if hasattr(sys, 'exc_clear'):
sys.exc_clear()

request_close = getattr(self.request, 'close', None)
if request_close is not None:
request_close()
clear_request = True
finally:
rv = _request_ctx_stack.pop()

# get rid of circular dependencies at the end of the request
# so that we don't require the GC to be active.
if clear_request:
rv.request.environ['werkzeug.request'] = None

# Get rid of the app as well if necessary.
if app_ctx is not None:
# ####################################################
app_ctx.pop(exc)

assert rv is self, 'Popped wrong request context. '
'(%r instead of %r)' % (rv, self)

def auto_pop(self, exc):
if self.request.environ.get('flask._preserve_context') or
(exc is not None and self.app.preserve_context_on_exception):
self.preserved = True
self._preserved_exc = exc
else:
self.pop(exc)

request_tearing_down

 

同上

 

同上

 

同上

 

同上

 

def flash(message, category='message'):
"""Flashes a message to the next request. In order to remove the
flashed message from the session and to display it to the user,
the template has to call :func:`get_flashed_messages`.

.. versionchanged:: 0.3
`category` parameter added.

:param message: the message to be flashed.
:param category: the category for the message. The following values
are recommended: ``'message'`` for any kind of message,
``'error'`` for errors, ``'info'`` for information
messages and ``'warning'`` for warnings. However any
kind of string can be used as category.
"""
# Original implementation:
#
# session.setdefault('_flashes', []).append((category, message))
#
# This assumed that changes made to mutable structures in the session are
# are always in sync with the session object, which is not true for session
# implementations that use external storage for keeping their keys/values.
flashes = session.get('_flashes', [])
flashes.append((category, message))
session['_flashes'] = flashes

# ############### 触发 message_flashed 信号 ###############
message_flashed.send(current_app._get_current_object(),
message=message, category=category)

message_flashed

内置信号使用

from flask import Flask,signals,render_template,flash


app = Flask(__name__)

def func1(*args,**kwargs):
    print('触发信号:request_started')

def func2(*args,**kwargs):
    print('触发信号:appcontext_pushed')

signals.request_started.connect(func1)
signals.appcontext_pushed.connect(func2)

@app.route('/login')
def login():
    return render_template('index.html')

if __name__ == '__main__':
    app.run()

触发信号时就会执行相应的函数

内置信号的顺序

appcontext_pushed = _signals.signal('appcontext-pushed')
request_started = _signals.signal('request-started')

如果有render:
    before_render_template = _signals.signal('before-render-template')
    template_rendered = _signals.signal('template-rendered')

request_finished = _signals.signal('request-finished')

如果视图函数有异常：
    got_request_exception = _signals.signal('got-request-exception')

request_tearing_down = _signals.signal('request-tearing-down')
appcontext_tearing_down = _signals.signal('appcontext-tearing-down')

appcontext_popped = _signals.signal('appcontext-popped')


如果使用信号：
    message_flashed = _signals.signal('message-flashed')

2. 自定义信号

#!/usr/bin/env python
# -*- coding:utf-8 -*-
from flask import Flask, current_app, flash, render_template
from flask.signals import _signals
 
app = Flask(import_name=__name__)
 
 
# 自定义信号
xxxxx = _signals.signal('xxxxx')
 
 
def func(sender, *args, **kwargs):
    print(sender)
 
# 自定义信号中注册函数
xxxxx.connect(func)
 
 
@app.route("/x")
def index():
    # 触发信号
    xxxxx.send('123123', k1='v1')
    return 'Index'
 
 
if __name__ == '__main__':
    app.run()

信号和before_request区别

before_request，可以控制请求是否可以继续往后执行。
信号，在原来的基础增加额外的操作和值。