Flask 上下文管理
flask的request和session设置方式比较新颖，如果没有这种方式，那么就只能通过参数的传递。
flask是如何做的呢？
1.Python 实现的本地线程
保证即使是多个线程，自己的值也是互相隔离。
import threading local_values = threading.local() def func(num): local_values.name = num import time time.sleep(1) print(local_values.name, threading.current_thread().name) for i in range(20): th = threading.Thread(target=func, args=(i,), name='线程%s' % i) th.start()
3. Flask内部实现的本地线程
Flask源码
自定义类似于本地线程
from flask import session try: from greenlet import getcurrent as get_ident except ImportError: try: from thread import get_ident except ImportError: from _thread import get_ident # 获取线程的唯一标识 get_ident() class Local(object): __slots__ = ('__storage__', '__ident_func__') def __init__(self): # self.__storage__ = {} # self.__ident_func__ = get_ident object.__setattr__(self, '__storage__', {}) object.__setattr__(self, '__ident_func__', get_ident) def __iter__(self): return iter(self.__storage__.items()) def __release_local__(self): self.__storage__.pop(self.__ident_func__(), None) def __getattr__(self, name): try: return self.__storage__[self.__ident_func__()][name] except KeyError: raise AttributeError(name) def __setattr__(self, name, value): ident = self.__ident_func__() # 获取当前线程(协程)的唯一标识 storage = self.__storage__ # {} try: storage[ident][name] = value # { 111:{'stack':[] },222:{'stack':[] } } except KeyError: storage[ident] = {name: value} def __delattr__(self, name): try: del self.__storage__[self.__ident_func__()][name] except KeyError: raise AttributeError(name) _local = Local() _local.stack = []
特殊栈
from flask import session try: from greenlet import getcurrent as get_ident except ImportError: try: from thread import get_ident except ImportError: from _thread import get_ident # 获取线程的唯一标识 get_ident() class Local(object): __slots__ = ('__storage__', '__ident_func__') def __init__(self): # self.__storage__ = {} # self.__ident_func__ = get_ident object.__setattr__(self, '__storage__', {}) object.__setattr__(self, '__ident_func__', get_ident) def __iter__(self): return iter(self.__storage__.items()) def __release_local__(self): self.__storage__.pop(self.__ident_func__(), None) def __getattr__(self, name): try: return self.__storage__[self.__ident_func__()][name] except KeyError: raise AttributeError(name) def __setattr__(self, name, value): ident = self.__ident_func__() # 获取当前线程(协程)的唯一标识 storage = self.__storage__ # {} try: storage[ident][name] = value # { 111:{'stack':[] },222:{'stack':[] } } except KeyError: storage[ident] = {name: value} def __delattr__(self, name): try: del self.__storage__[self.__ident_func__()][name] except KeyError: raise AttributeError(name) class LocalStack(object): def __init__(self): self._local = Local() def __release_local__(self): self._local.__release_local__() def _get__ident_func__(self): return self._local.__ident_func__ def _set__ident_func__(self, value): object.__setattr__(self._local, '__ident_func__', value) __ident_func__ = property(_get__ident_func__, _set__ident_func__) del _get__ident_func__, _set__ident_func__ def __call__(self): def _lookup(): rv = self.top if rv is None: raise RuntimeError('object unbound') return rv return LocalProxy(_lookup) def push(self, obj): """Pushes a new item to the stack""" rv = getattr(self._local, 'stack', None) if rv is None: """ self._local= { 唯一标示: {'stack':[]} } """ self._local.stack = rv = [] rv.append(obj) return rv def pop(self): """Removes the topmost item from the stack, will return the old value or `None` if the stack was already empty. """ # [] stack = getattr(self._local, 'stack', None) if stack is None: return None elif len(stack) == 1: #release_local(self._local) return stack[-1] else: return stack.pop() @property def top(self): """The topmost item on the stack. If the stack is empty, `None` is returned. """ try: return self._local.stack[-1] except (AttributeError, IndexError): return None _request_ctx_stack = LocalStack()
利用flask源码中的stack和local
from functools import partial from flask.globals import LocalStack, LocalProxy _request_ctx_stack = LocalStack() class RequestContext(object): def __init__(self, environ): self.request = environ def _lookup_req_object(name): top = _request_ctx_stack.top if top is None: raise RuntimeError(_request_ctx_stack) return getattr(top, name) # 实例化了LocalProxy对象，_lookup_req_object参数传递 session = LocalProxy(partial(_lookup_req_object, 'session')) """ local = { “标识”: {'stack': [RequestContext(),]} } """ _request_ctx_stack.push(RequestContext('c1')) # 当请求进来时，放入 print(session) # 获取 RequestContext('c1')， top方法 print(session) # 获取 RequestContext('c1')， top方法 _request_ctx_stack.pop() # 请求结束pop
查看Flask源码Local.py,global.by,以及app.__call__方法 更清晰
# -*- coding: utf-8 -*- """ flask.globals ~~~~~~~~~~~~~ Defines all the global objects that are proxies to the current active context. :copyright: (c) 2015 by Armin Ronacher. :license: BSD, see LICENSE for more details. """ from functools import partial from werkzeug.local import LocalStack, LocalProxy _request_ctx_err_msg = '''\ Working outside of request context. This typically means that you attempted to use functionality that needed an active HTTP request. Consult the documentation on testing for information about how to avoid this problem.\ ''' _app_ctx_err_msg = '''\ Working outside of application context. This typically means that you attempted to use functionality that needed to interface with the current application object in a way. To solve this set up an application context with app.app_context(). See the documentation for more information.\ ''' def _lookup_req_object(name): top = _request_ctx_stack.top if top is None: raise RuntimeError(_request_ctx_err_msg) return getattr(top, name) def _lookup_app_object(name): top = _app_ctx_stack.top if top is None: raise RuntimeError(_app_ctx_err_msg) return getattr(top, name) def _find_app(): top = _app_ctx_stack.top if top is None: raise RuntimeError(_app_ctx_err_msg) return top.app # context locals _request_ctx_stack = LocalStack() _app_ctx_stack = LocalStack() current_app = LocalProxy(_find_app) request = LocalProxy(partial(_lookup_req_object, 'request')) session = LocalProxy(partial(_lookup_req_object, 'session')) g = LocalProxy(partial(_lookup_app_object, 'g'))
# -*- coding: utf-8 -*- """ werkzeug.local ~~~~~~~~~~~~~~ This module implements context-local objects. :copyright: (c) 2014 by the Werkzeug Team, see AUTHORS for more details. :license: BSD, see LICENSE for more details. """ import copy from functools import update_wrapper from werkzeug.wsgi import ClosingIterator from werkzeug._compat import PY2, implements_bool # since each thread has its own greenlet we can just use those as identifiers # for the context. If greenlets are not available we fall back to the # current thread ident depending on where it is. try: from greenlet import getcurrent as get_ident except ImportError: try: from thread import get_ident except ImportError: from _thread import get_ident def release_local(local): """Releases the contents of the local for the current context. This makes it possible to use locals without a manager. Example:: >>> loc = Local() >>> loc.foo = 42 >>> release_local(loc) >>> hasattr(loc, 'foo') False With this function one can release :class:`Local` objects as well as :class:`LocalStack` objects. However it is not possible to release data held by proxies that way, one always has to retain a reference to the underlying local object in order to be able to release it. .. versionadded:: 0.6.1 """ local.__release_local__() class Local(object): __slots__ = ('__storage__', '__ident_func__') def __init__(self): #不用self是因为后面有__setattr__和__getattr__,防止死循环 object.__setattr__(self, '__storage__', {}) object.__setattr__(self, '__ident_func__', get_ident) def __iter__(self): return iter(self.__storage__.items()) def __call__(self, proxy): """Create a proxy for a name.""" return LocalProxy(self, proxy) def __release_local__(self): self.__storage__.pop(self.__ident_func__(), None) def __getattr__(self, name): try: return self.__storage__[self.__ident_func__()][name] except KeyError: raise AttributeError(name) # 设置值 ''' storage:{ self.__ident_func__():{ name:value } } ''' def __setattr__(self, name, value): ident = self.__ident_func__() storage = self.__storage__ try: storage[ident][name] = value except KeyError: storage[ident] = {name: value} def __delattr__(self, name): try: del self.__storage__[self.__ident_func__()][name] except KeyError: raise AttributeError(name) class LocalStack(object): """This class works similar to a :class:`Local` but keeps a stack of objects instead. This is best explained with an example:: >>> ls = LocalStack() >>> ls.push(42) >>> ls.top 42 >>> ls.push(23) >>> ls.top 23 >>> ls.pop() 23 >>> ls.top 42 They can be force released by using a :class:`LocalManager` or with the :func:`release_local` function but the correct way is to pop the item from the stack after using. When the stack is empty it will no longer be bound to the current context (and as such released). By calling the stack without arguments it returns a proxy that resolves to the topmost item on the stack. .. versionadded:: 0.6.1 """ def __init__(self): self._local = Local() def __release_local__(self): self._local.__release_local__() def _get__ident_func__(self): return self._local.__ident_func__ def _set__ident_func__(self, value): object.__setattr__(self._local, '__ident_func__', value) __ident_func__ = property(_get__ident_func__, _set__ident_func__) del _get__ident_func__, _set__ident_func__ def __call__(self): def _lookup(): rv = self.top if rv is None: raise RuntimeError('object unbound') return rv return LocalProxy(_lookup) def push(self, obj): """Pushes a new item to the stack""" rv = getattr(self._local, 'stack', None) if rv is None: self._local.stack = rv = [] rv.append(obj) return rv def pop(self): """Removes the topmost item from the stack, will return the old value or `None` if the stack was already empty. """ stack = getattr(self._local, 'stack', None) if stack is None: return None elif len(stack) == 1: release_local(self._local) return stack[-1] else: return stack.pop() @property def top(self): """The topmost item on the stack. If the stack is empty, `None` is returned. """ try: return self._local.stack[-1] except (AttributeError, IndexError): return None class LocalManager(object): """Local objects cannot manage themselves. For that you need a local manager. You can pass a local manager multiple locals or add them later by appending them to `manager.locals`. Every time the manager cleans up, it will clean up all the data left in the locals for this context. The `ident_func` parameter can be added to override the default ident function for the wrapped locals. .. versionchanged:: 0.6.1 Instead of a manager the :func:`release_local` function can be used as well. .. versionchanged:: 0.7 `ident_func` was added. """ def __init__(self, locals=None, ident_func=None): if locals is None: self.locals = [] elif isinstance(locals, Local): self.locals = [locals] else: self.locals = list(locals) if ident_func is not None: self.ident_func = ident_func for local in self.locals: object.__setattr__(local, '__ident_func__', ident_func) else: self.ident_func = get_ident def get_ident(self): """Return the context identifier the local objects use internally for this context. You cannot override this method to change the behavior but use it to link other context local objects (such as SQLAlchemy's scoped sessions) to the Werkzeug locals. .. versionchanged:: 0.7 You can pass a different ident function to the local manager that will then be propagated to all the locals passed to the constructor. """ return self.ident_func() def cleanup(self): """Manually clean up the data in the locals for this context. Call this at the end of the request or use `make_middleware()`. """ for local in self.locals: release_local(local) def make_middleware(self, app): """Wrap a WSGI application so that cleaning up happens after request end. """ def application(environ, start_response): return ClosingIterator(app(environ, start_response), self.cleanup) return application def middleware(self, func): """Like `make_middleware` but for decorating functions. Example usage:: @manager.middleware def application(environ, start_response): ... The difference to `make_middleware` is that the function passed will have all the arguments copied from the inner application (name, docstring, module). """ return update_wrapper(self.make_middleware(func), func) def __repr__(self): return '<%s storages: %d>' % ( self.__class__.__name__, len(self.locals) ) @implements_bool class LocalProxy(object): """Acts as a proxy for a werkzeug local. Forwards all operations to a proxied object. The only operations not supported for forwarding are right handed operands and any kind of assignment. Example usage:: from werkzeug.local import Local l = Local() # these are proxies request = l('request') user = l('user') from werkzeug.local import LocalStack _response_local = LocalStack() # this is a proxy response = _response_local() Whenever something is bound to l.user / l.request the proxy objects will forward all operations. If no object is bound a :exc:`RuntimeError` will be raised. To create proxies to :class:`Local` or :class:`LocalStack` objects, call the object as shown above. If you want to have a proxy to an object looked up by a function, you can (as of Werkzeug 0.6.1) pass a function to the :class:`LocalProxy` constructor:: session = LocalProxy(lambda: get_current_request().session) .. versionchanged:: 0.6.1 The class can be instantiated with a callable as well now. """ __slots__ = ('__local', '__dict__', '__name__', '__wrapped__') def __init__(self, local, name=None): object.__setattr__(self, '_LocalProxy__local', local) object.__setattr__(self, '__name__', name) if callable(local) and not hasattr(local, '__release_local__'): # "local" is a callable that is not an instance of Local or # LocalManager: mark it as a wrapped function. object.__setattr__(self, '__wrapped__', local) def _get_current_object(self): """Return the current object. This is useful if you want the real object behind the proxy at a time for performance reasons or because you want to pass the object into a different context. """ if not hasattr(self.__local, '__release_local__'): return self.__local() try: return getattr(self.__local, self.__name__) except AttributeError: raise RuntimeError('no object bound to %s' % self.__name__) @property def __dict__(self): try: return self._get_current_object().__dict__ except RuntimeError: raise AttributeError('__dict__') def __repr__(self): try: obj = self._get_current_object() except RuntimeError: return '<%s unbound>' % self.__class__.__name__ return repr(obj) def __bool__(self): try: return bool(self._get_current_object()) except RuntimeError: return False def __unicode__(self): try: return unicode(self._get_current_object()) # noqa except RuntimeError: return repr(self) def __dir__(self): try: return dir(self._get_current_object()) except RuntimeError: return [] def __getattr__(self, name): if name == '__members__': return dir(self._get_current_object()) return getattr(self._get_current_object(), name) def __setitem__(self, key, value): self._get_current_object()[key] = value def __delitem__(self, key): del self._get_current_object()[key] if PY2: __getslice__ = lambda x, i, j: x._get_current_object()[i:j] def __setslice__(self, i, j, seq): self._get_current_object()[i:j] = seq def __delslice__(self, i, j): del self._get_current_object()[i:j] __setattr__ = lambda x, n, v: setattr(x._get_current_object(), n, v) __delattr__ = lambda x, n: delattr(x._get_current_object(), n) __str__ = lambda x: str(x._get_current_object()) __lt__ = lambda x, o: x._get_current_object() < o __le__ = lambda x, o: x._get_current_object() <= o __eq__ = lambda x, o: x._get_current_object() == o __ne__ = lambda x, o: x._get_current_object() != o __gt__ = lambda x, o: x._get_current_object() > o __ge__ = lambda x, o: x._get_current_object() >= o __cmp__ = lambda x, o: cmp(x._get_current_object(), o) # noqa __hash__ = lambda x: hash(x._get_current_object()) __call__ = lambda x, *a, **kw: x._get_current_object()(*a, **kw) __len__ = lambda x: len(x._get_current_object()) __getitem__ = lambda x, i: x._get_current_object()[i] __iter__ = lambda x: iter(x._get_current_object()) __contains__ = lambda x, i: i in x._get_current_object() __add__ = lambda x, o: x._get_current_object() + o __sub__ = lambda x, o: x._get_current_object() - o __mul__ = lambda x, o: x._get_current_object() * o __floordiv__ = lambda x, o: x._get_current_object() // o __mod__ = lambda x, o: x._get_current_object() % o __divmod__ = lambda x, o: x._get_current_object().__divmod__(o) __pow__ = lambda x, o: x._get_current_object() ** o __lshift__ = lambda x, o: x._get_current_object() << o __rshift__ = lambda x, o: x._get_current_object() >> o __and__ = lambda x, o: x._get_current_object() & o __xor__ = lambda x, o: x._get_current_object() ^ o __or__ = lambda x, o: x._get_current_object() | o __div__ = lambda x, o: x._get_current_object().__div__(o) __truediv__ = lambda x, o: x._get_current_object().__truediv__(o) __neg__ = lambda x: -(x._get_current_object()) __pos__ = lambda x: +(x._get_current_object()) __abs__ = lambda x: abs(x._get_current_object()) __invert__ = lambda x: ~(x._get_current_object()) __complex__ = lambda x: complex(x._get_current_object()) __int__ = lambda x: int(x._get_current_object()) __long__ = lambda x: long(x._get_current_object()) # noqa __float__ = lambda x: float(x._get_current_object()) __oct__ = lambda x: oct(x._get_current_object()) __hex__ = lambda x: hex(x._get_current_object()) __index__ = lambda x: x._get_current_object().__index__() __coerce__ = lambda x, o: x._get_current_object().__coerce__(x, o) __enter__ = lambda x: x._get_current_object().__enter__() __exit__ = lambda x, *a, **kw: x._get_current_object().__exit__(*a, **kw) __radd__ = lambda x, o: o + x._get_current_object() __rsub__ = lambda x, o: o - x._get_current_object() __rmul__ = lambda x, o: o * x._get_current_object() __rdiv__ = lambda x, o: o / x._get_current_object() if PY2: __rtruediv__ = lambda x, o: x._get_current_object().__rtruediv__(o) else: __rtruediv__ = __rdiv__ __rfloordiv__ = lambda x, o: o // x._get_current_object() __rmod__ = lambda x, o: o % x._get_current_object() __rdivmod__ = lambda x, o: x._get_current_object().__rdivmod__(o) __copy__ = lambda x: copy.copy(x._get_current_object()) __deepcopy__ = lambda x, memo: copy.deepcopy(x._get_current_object(), memo)
