Flask系列(六)Flask實例化補充及信號

1、實例化補充

instance_path和instance_relative_config是配合來用的。

這兩個參數是用來找配置文件的，當用app.config.from_pyfile('settings.py')這種方式導入配置文件的時候會用到

from flask import Flask,request
app = Flask(__name__,instance_path=None, instance_relative_config=True)
app.config.from_pyfile('settings.py')
# instsnce_path：#若是配置了instance_path，就會去找instance裏面的文件
# instance_relative_config： #若是設置爲True，配置文件就找不到了，就會去找instance裏面的settings.py
app.open_session
print(app.config.get("NNN"))
@app.route('/index') # app.route('/index')  f(index)
def index():
    print(request)
    return "xx"

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

 若是設置了instance_releative_config = True，就找不着settings.py文件了，解決辦法：就手動建立一個instance的文件夾

2、信號（blinker）

一、flask的內置信號

Flask框架中的信號基於blinker，其主要就是讓開發者但是在flask請求過程當中定製一些用戶行爲。說白了也就是flask在列表裏面

預留了幾個空列表，在裏面存東西。信號經過發送通知來幫助你解耦應用。簡言之，信號容許某個發送者通知接收者有事情發生了；、

10個信號：
 2. request_started = _signals.signal('request-started')                # 請求到來前執行
 5. request_finished = _signals.signal('request-finished')              # 請求結束後執行
                 
 3. before_render_template = _signals.signal('before-render-template')  # 模板渲染前執行
 4. template_rendered = _signals.signal('template-rendered')            # 模板渲染後執行
                 
 執行2/3/4/5或不執行時出現異常 got_request_exception = _signals.signal('got-request-exception')    # 請求執行出現異常時執行
                 
 6. request_tearing_down = _signals.signal('request-tearing-down')      # 請求執行完畢後自動執行（不管成功與否）
 7. appcontext_tearing_down = _signals.signal('appcontext-tearing-down')# 請求上下文執行完畢後自動執行（不管成功與否）
                 
                 
 1. appcontext_pushed = _signals.signal('appcontext-pushed')            # 請求app上下文push時執行
                
 8. appcontext_popped = _signals.signal('appcontext-popped')            # 請求上下文pop時執行
                
 message_flashed = _signals.signal('message-flashed')        # 調用flask在其中添加數據時，自動觸發

問題1：特殊的裝飾器（@app.before_first_request ；@app.before_request ； @app.after_request）和信號有什麼區別？

　　　-  觸發信號是沒有返回值的，寫不寫返回值都無所謂

　　　-  特殊的裝飾器對返回值是有意義的，當before_request有返回值時就不會執行後續視圖函數了，沒有返回值的時候纔會執行後續函數，而after_request必須有返回值 

　　       因此特殊裝飾器的功能比信號的功能強大

問題2：經過信號能夠作權限嗎？

　　　- 自己是作不了的，要想作得用其餘的機制配合着來使用，這樣作的話會閒的很麻煩，因此咱們選擇中間件來作

問題3：信號用於作什麼呢？

　　　- 只作一些自定義的操做，並且沒有返回值

 　　  - 下降代碼之間的耦合

flask內置信號源碼詳細

class Flask(_PackageBoundObject):

    def full_dispatch_request(self):
       
        self.try_trigger_before_first_request_functions()
        try:
            # ############### 觸發request_started 信號 ###############
            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 信號 ###############
        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)

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 信號 ###############
    before_render_template.send(app, template=template, context=context)
    rv = template.render(context)
    
    # ############### template_rendered 信號 ###############
    template_rendered.send(app, template=template, context=context)
    return rv

同上

class Flask(_PackageBoundObject):

    def handle_exception(self, e):
       
        exc_type, exc_value, tb = sys.exc_info()

        # ############### got_request_exception 信號 ###############
        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
                # 這裏這裏這裏這裏這裏這裏這裏這裏這裏這裏這裏這裏 #
                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)
        # ############## 觸發 appcontext_pushed 信號 ##############
        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]
                # ############## 觸發 appcontext_tearing_down 信號 ##############
                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)

        # ############## 觸發 appcontext_popped 信號 ##############
        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]

                # ################## 觸發 request_tearing_down 信號 ##################
                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)

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

    # ############### 觸發 message_flashed 信號 ###############
    message_flashed.send(current_app._get_current_object(),
                         message=message, category=category)

二、自定義信號（Blinker的使用）

　　第一步：建立信號

　　第二步：將函數註冊到信號中： 添加到這個列表

　　第三步： 發送信號

　　第四步：運行

具體實現：可參考flask源碼，寫一個自定義信號

from flask import Flask,flash
from flask.signals import _signals
app = Flask(__name__)

xinhao = _signals.signal("xinhao")#建立信號
#定義函數
def wahaha(*args,**kwargs):
    print("娃哈哈",args,kwargs)

def sww(*args,**kwargs):
    print("爽歪歪",args,kwargs)
# 將函數註冊到信號中,添加到這個列表
xinhao.connect(wahaha)
xinhao.connect(sww)

@app.route("/zzz")
def zzz():
    xinhao.send(sender='xxx',a1=123,a2=456)  #觸發這個信號，執行註冊到列表中的全部函數,這裏的參數個上面函數的參數一致
    return "發送信號成功"

if __name__ == '__main__':
    app.run(debug=True)
    
#打印結果
# 娃哈哈 (None,) {'sender': 'xxx', 'a1': 123, 'a2': 456}
# 爽歪歪 (None,) {'sender': 'xxx', 'a1': 123, 'a2': 456}

3、chain模塊簡單的測試

v1 = [11,22,33,44]
v2 = [1,4,7,5]
from itertools import chain
ff = []
for i in chain(v1,v2):   #chain會把兩個列表鏈接在一塊
    ff.append(i)
print(ff)     #[11, 22, 33, 44, 1, 4, 7, 5]