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
2. 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)
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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
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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)
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)
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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)
3. 执行流程
a. before_first_request 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 f. session.save_session() g. 触发 request_finished信号 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
4. 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()