Flask进阶信号的使用和源码剖析
进阶知识点
信号
flask的内置信号、
from flask import signals
知识点
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。
必须注册 并且下载blinker模块
pip3 install blinker #
内置10个信号和
预留的局部钩子
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）
#需要手动触发 进行push pop的时候 用于上下文管理
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flash存值之后只能取一次
信号和中间件的执行流程
a. before_first_request #请求开始
b. 触发 request_started 信号
c. before_request
d. 模板渲染
渲染前的信号 before_render_template.send(app, template=template, context=context)
rv = template.render(context) # 模板渲染
渲染后的信号 template_rendered.send(app, template=template, context=context)
e. after_request #视图结束
f. session.save_session()#存储session
g. 触发 request_finished信号 #请求结束
如果上述过程出错：
触发错误处理信号 got_request_exception.send(self, exception=e)
h. 触发信号 request_tearing_down
信号的源码和扩展点
1.在中间件中手动预留钩子
from flask import Flask,render_template
app = Flask(__name__)
@app.route('/index')
def index():
return render_template('index.html')
@app.route('/order')
def order():
return render_template('order.html')
class MyMiddleware(object):
def __init__(self,old_app):
self.wsgi_app = old_app.wsgi_app
def __call__(self, *args, **kwargs):
print('123')
result = self.wsgi_app(*args, **kwargs)
print('456')
return result
app.wsgi_app = MyMiddleware(app)
if __name__ == '__main__':
app.run()
2. before_first_request #第一次请求开始
有且执行一次
源码
注意执行
#寻找流程
1.项目启动执行app(flask实例化对象).run()
2. run_simple(host, port, self, **options)
3.执行self() call方法
4.执行wsgi_app
5.执行full_dispatch_reqeust
6.self.try_trigger_before_first_request_functions()
for func in self.before_first_request_funcs:
func()
使用示例
from flask import Flask,render_template
app = Flask(__name__)
@app.before_first_request
def f2():
print('before_first_requestf2被触发')
@app.route('/index')
def index():
return render_template('index.html')
@app.route('/order')
def order():
return render_template('order.html')
if __name__ == '__main__':
app.run()
3. 触发 request_started 信号
源码
#源码寻找流程
1.项目启动执行app(flask实例化对象).run()
2. run_simple(host, port, self, **options)
3.执行self() call方法
4.执行wsgi_app 执行full_dispatch_request
5. def full_dispatch_request(self):
request_started.send(self)
使用示例
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@app.url_value_preprocessor
def f5(endpoint,args):
print('f5')
@app.route('/index/')
def index():
print('index')
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
4.url_value_processor
源码流程
#源码寻找流程
1.项目启动执行app(flask实例化对象).run()
2. run_simple(host, port, self, **options)
3.执行self() call方法
4.执行wsgi_app 执行full_dispatch_request
5. def full_dispatch_request(self):
request_started.send(self)
rv = self.preprocess_request()
6. def preprocess_request(self):
bp = _request_ctx_stack.top.request.blueprint
funcs = self.url_value_preprocessors.get(None, ())
if bp is not None and bp in self.url_value_preprocessors:
funcs = chain(funcs, self.url_value_preprocessors[bp])
for func in funcs:
func(request.endpoint, request.view_args)
使用示例
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@app.url_value_preprocessor
def f5(endpoint,args):
print('f5')
@app.route('/index/')
def index():
print('index')
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
5 before_reuqest
源码流程
#源码寻找流程
1.项目启动执行app(flask实例化对象).run()
2. run_simple(host, port, self, **options)
3.执行self() call方法
4.执行wsgi_app 执行full_dispatch_request
5. def full_dispatch_request(self):
request_started.send(self)
rv = self.preprocess_request()
6. def preprocess_request(self):
bp = _request_ctx_stack.top.request.blueprint
funcs = self.url_value_preprocessors.get(None, ())
if bp is not None and bp in self.url_value_preprocessors:
funcs = chain(funcs, self.url_value_preprocessors[bp])
for func in funcs:
func(request.endpoint, request.view_args)
funcs = self.before_request_funcs.get(None, ())
if bp is not None and bp in self.before_request_funcs:
funcs = chain(funcs, self.before_request_funcs[bp])
for func in funcs:
rv = func()
if rv is not None:
return rv
使用示例
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@app.before_request
def f6():
g.xx = 123
print('f6')
@app.route('/index/')
def index():
print('index')
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
6.识图函数之后
模板渲染
before_render_template / rendered_template
源码
@account.route('/login')
def login():
return render_template('login.html')
def render_template(template_name_or_list, **context):
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
使用
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@signals.before_render_template.connect
def f7(app, template, context):
print('f7')
@signals.template_rendered.connect
def f8(app, template, context):
print('f8')
@app.route('/index/')
def index():
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
7.after_request
源码
def process_response(self, response):
if None in self.after_request_funcs:
funcs = chain(funcs, reversed(self.after_request_funcs[None]))
使用
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@app.after_request
def f9(response):
print('f9')
return response
@app.route('/index/')
def index():
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
8.got_request_exception 触发
源码
项目启动执行app(flask实例化对象).run()
2. run_simple(host, port, self, **options)
3.执行self() call方法
4. def wsgi_app(self, environ, start_response):
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))
使用
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@app.before_first_request
def test():
int('asdf')
@signals.got_request_exception.connect
def f11(app,exception):
print('f11')
@app.route('/index/')
def index():
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
10.request_tearing_down,
使用
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@signals.request_tearing_down.connect
def f13(app,exc):
print('f13')
@app.route('/index/')
def index():
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
11.appcontext_tearing_down,
9. appcontext_pushed,
12.appcontext_popped
使用
from flask import Flask,render_template,g
from flask import signals
app = Flask(__name__)
@signals.appcontext_popped.connect
def f14(app):
print('f14')
@app.route('/index/')
def index():
return render_template('index.html')
@app.route('/order')
def order():
print('order')
return render_template('order.html')
if __name__ == '__main__':
app.run()
总体源码
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)
c. before_request
d. 模板渲染
渲染前的信号 before_render_template.send(app, template=template, context=context)
rv = template.render(context) # 模板渲染
渲染后的信号 template_rendered.send(app, template=template, context=context)
e. after_request #视图结束
f. session.save_session()#存储session
g. 触发 request_finished信号 #请求结束
如果上述过程出错：
触发错误处理信号 got_request_exception.send(self, exception=e)
h. 触发信号 request_tearing_down
13.message_flashed
源码流程
def flash(message, category='message'):
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
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