Flask中信号的使用
1、Flask中信号简介
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。
2、内置信号
Flask中内置信号在·signals.py中定义：
1 template_rendered = _signals.signal('template-rendered') # 模板渲染后执行 2 before_render_template = _signals.signal('before-render-template') # 模板渲染前执行 3 request_started = _signals.signal('request-started') # 请求到来前执行 4 request_finished = _signals.signal('request-finished') # 请求结束后执行 5 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） 6 got_request_exception = _signals.signal('got-request-exception') # 请求执行出现异常时执行 7 appcontext_tearing_down = _signals.signal('appcontext-tearing-down') # 应用上下文执行完毕后自动执行（无论成功与否） 8 appcontext_pushed = _signals.signal('appcontext-pushed') # 应用上下文push时执行 9 appcontext_popped = _signals.signal('appcontext-popped') # 应用上下文pop时执行 10 message_flashed = _signals.signal('message-flashed') # 调用flash在其中添加数据时，自动触发
源码示例：
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
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
class Flask(_PackageBoundObject): def full_dispatch_request(self): """Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling. .. versionadded:: 0.7 """ 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) return self.finalize_request(rv) def finalize_request(self, rv, from_error_handler=False): """Given the return value from a view function this finalizes the request by converting it into a response and invoking the postprocessing functions. This is invoked for both normal request dispatching as well as error handlers. Because this means that it might be called as a result of a failure a special safe mode is available which can be enabled with the `from_error_handler` flag. If enabled, failures in response processing will be logged and otherwise ignored. :internal: """ response = self.make_response(rv) try: response = self.process_response(response) # ############### request_finished 信号 ############### request_finished.send(self, response=response) except Exception: if not from_error_handler: raise self.logger.exception('Request finalizing failed with an ' 'error while handling an error') return response def wsgi_app(self, environ, start_response): """The actual WSGI application. This is not implemented in :meth:`__call__` so that middlewares can be applied without losing a reference to the app object. Instead of doing this:: app = MyMiddleware(app) It's a better idea to do this instead:: app.wsgi_app = MyMiddleware(app.wsgi_app) Then you still have the original application object around and can continue to call methods on it. .. versionchanged:: 0.7 Teardown events for the request and app contexts are called even if an unhandled error occurs. Other events may not be called depending on when an error occurs during dispatch. See :ref:`callbacks-and-errors`. :param environ: A WSGI environment. :param start_response: A callable accepting a status code, a list of headers, and an optional exception context to start the response. """ ctx = self.request_context(environ) error = None try: try: ctx.push() response = self.full_dispatch_request() except Exception as e: error = e response = self.handle_exception(e) except: error = sys.exc_info()[1] raise return response(environ, start_response) finally: if self.should_ignore_error(error): error = None ctx.auto_pop(error)
class Flask(_PackageBoundObject): def full_dispatch_request(self): """Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling. .. versionadded:: 0.7 """ 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) return self.finalize_request(rv) def finalize_request(self, rv, from_error_handler=False): """Given the return value from a view function this finalizes the request by converting it into a response and invoking the postprocessing functions. This is invoked for both normal request dispatching as well as error handlers. Because this means that it might be called as a result of a failure a special safe mode is available which can be enabled with the `from_error_handler` flag. If enabled, failures in response processing will be logged and otherwise ignored. :internal: """ response = self.make_response(rv) try: response = self.process_response(response) # ############### request_finished 信号 ############### request_finished.send(self, response=response) except Exception: if not from_error_handler: raise self.logger.exception('Request finalizing failed with an ' 'error while handling an error') return response def wsgi_app(self, environ, start_response): """The actual WSGI application. This is not implemented in :meth:`__call__` so that middlewares can be applied without losing a reference to the app object. Instead of doing this:: app = MyMiddleware(app) It's a better idea to do this instead:: app.wsgi_app = MyMiddleware(app.wsgi_app) Then you still have the original application object around and can continue to call methods on it. .. versionchanged:: 0.7 Teardown events for the request and app contexts are called even if an unhandled error occurs. Other events may not be called depending on when an error occurs during dispatch. See :ref:`callbacks-and-errors`. :param environ: A WSGI environment. :param start_response: A callable accepting a status code, a list of headers, and an optional exception context to start the response. """ ctx = self.request_context(environ) error = None try: try: ctx.push() response = self.full_dispatch_request() except Exception as e: error = e response = self.handle_exception(e) except: error = sys.exc_info()[1] raise return response(environ, start_response) finally: if self.should_ignore_error(error): error = None ctx.auto_pop(error)
class RequestContext(object): def __init__(self, app, environ, request=None): self.app = app if request is None: request = app.request_class(environ) self.request = request self.url_adapter = app.create_url_adapter(self.request) self.flashes = None self.session = None self._implicit_app_ctx_stack = [] self.preserved = False self._preserved_exc = None self._after_request_functions = [] self.match_request() 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] ################################################### self.app.do_teardown_request(exc) 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() 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) class Flask(_PackageBoundObject): def do_teardown_request(self, exc=_sentinel): if exc is _sentinel: exc = sys.exc_info()[1] funcs = reversed(self.teardown_request_funcs.get(None, ())) bp = _request_ctx_stack.top.request.blueprint if bp is not None and bp in self.teardown_request_funcs: funcs = chain(funcs, reversed(self.teardown_request_funcs[bp])) for func in funcs: func(exc) # ################## 触发 request_tearing_down 信号 ################## request_tearing_down.send(self, exc=exc)
class Flask(_PackageBoundObject): def handle_exception(self, e): """Default exception handling that kicks in when an exception occurs that is not caught. In debug mode the exception will be re-raised immediately, otherwise it is logged and the handler for a 500 internal server error is used. If no such handler exists, a default 500 internal server error message is displayed. .. versionadded:: 0.3 """ 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 self.finalize_request(handler(e), from_error_handler=True)
class Flask(_PackageBoundObject): def do_teardown_appcontext(self, exc=_sentinel): """Called right before the application context is popped. When handling a request, the application context is popped after the request context. See :meth:`do_teardown_request`. This calls all functions decorated with :meth:`teardown_appcontext`. Then the :data:`appcontext_tearing_down` signal is sent. This is called by :meth:`AppContext.pop() <flask.ctx.AppContext.pop>`. .. versionadded:: 0.9 """ if exc is _sentinel: exc = sys.exc_info()[1] for func in reversed(self.teardown_appcontext_funcs): func(exc) # ############## 触发 appcontext_tearing_down 信号 ############## appcontext_tearing_down.send(self, exc=exc)
class AppContext(object): """The application context binds an application object implicitly to the current thread or greenlet, similar to how the :class:`RequestContext` binds request information. The application context is also implicitly created if a request context is created but the application is not on top of the individual application context. """ def __init__(self, app): self.app = app self.url_adapter = app.create_url_adapter(None) self.g = app.app_ctx_globals_class() # Like request context, app contexts can be pushed multiple times # but there a basic "refcount" is enough to track them. self._refcnt = 0 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] 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) def __enter__(self): self.push() return self def __exit__(self, exc_type, exc_value, tb): self.pop(exc_value) if BROKEN_PYPY_CTXMGR_EXIT and exc_type is not None: reraise(exc_type, exc_value, tb)
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 # 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 message_flashed.send(current_app._get_current_object(),
3、自定义信号
from flask import Flask,current_app,flash,render_template from flask.signals import _signals app = Flask(import_name=__name__) # 自定义信号 xxxx = _signals.signal('xxxx') def func(sender, *args, **kwargs): print(sender) # 自定义信号中注册函数 xxxx.connect(func) @app.route('/x') def index(): # 触发信号 xxxx.send("12345",k1="v1") return "Index" if __name__ == '__main__': app.run()
执行结果：
127.0.0.1 - - [07/Dec/2018 11:25:00] "GET / HTTP/1.1" 404 - 127.0.0.1 - - [07/Dec/2018 11:25:15] "GET /x HTTP/1.1" 200 - 12345
