Flask<3>--Context-Management

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Context Management

1 Storage Management

Flask support Coroutines by dict and greenlet.getcurrent, it allocates space for each greenlet and store them in a dictionary

  1. create a dictionary called __storage__
  2. set, get from __storage__ using greenlet.getcurrent as key
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try:
    from greenlet import getcurrent as get_ident
except ImportError:
    try:
        from thread import get_ident
    except ImportError:
        from _thread import get_ident

class Local(object):
    __slots__ = ('__storage__', '__ident_func__')

    def __init__(self):
        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)

    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)

2 Request Context

  • Request context includes request and session
  • Basically, each request comes
    1. Capsulate environ into a RequestContext object
    2. Add it into __storage__ dictionary
    3. Dispatch request to each view file and do operation
    4. Remove it from __storage__ dictionary

Picture for step 1, 2, 4

RequestContext

Picture for step 3 example

Request

partial(): it is quite funcional programming
object.__setattr__(self, '_LocalProxy__local', local): stuck here for quite a while. python3 documentation

3 App Context

  • It is quite similar as Request Context
  • It includes current_app and g