local.py

# -*- coding: utf-8 -*-
"""
    werkzeug.local
    ~~~~~~~~~~~~~~

    This module implements context-local objects.

    :copyright: (c) 2010 by the Werkzeug Team, see AUTHORS for more details.
    :license: BSD, see LICENSE for more details.
"""
try:
    from greenlet import getcurrent as get_current_greenlet
except ImportError: # pragma: no cover
    try:
        from py.magic import greenlet
        get_current_greenlet = greenlet.getcurrent
        del greenlet
    except:
        # catch all, py.* fails with so many different errors.
        get_current_greenlet = int
try:
    from thread import get_ident as get_current_thread, allocate_lock
except ImportError: # pragma: no cover
    from dummy_thread import get_ident as get_current_thread, allocate_lock

from werkzeug.wsgi import ClosingIterator
from werkzeug._internal import _patch_wrapper


# get the best ident function.  if greenlets are not installed we can
# safely just use the builtin thread function and save a python methodcall
# and the cost of calculating a hash.
if get_current_greenlet is int: # pragma: no cover
    get_ident = get_current_thread
else:
    get_ident = lambda: (get_current_thread(), get_current_greenlet())


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:`StackLocal` 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__', '__lock__')

    def __init__(self):
        object.__setattr__(self, '__storage__', {})
        object.__setattr__(self, '__lock__', allocate_lock())

    def __iter__(self):
        return self.__storage__.iteritems()

    def __call__(self, proxy):
        """Create a proxy for a name."""
        return LocalProxy(self, proxy)

    def __release_local__(self):
        self.__storage__.pop(get_ident(), None)

    def __getattr__(self, name):
        self.__lock__.acquire()
        try:
            try:
                return self.__storage__[get_ident()][name]
            except KeyError:
                raise AttributeError(name)
        finally:
            self.__lock__.release()

    def __setattr__(self, name, value):
        self.__lock__.acquire()
        try:
            ident = get_ident()
            storage = self.__storage__
            if ident in storage:
                storage[ident][name] = value
            else:
                storage[ident] = {name: value}
        finally:
            self.__lock__.release()

    def __delattr__(self, name):
        self.__lock__.acquire()
        try:
            try:
                del self.__storage__[get_ident()][name]
            except KeyError:
                raise AttributeError(name)
        finally:
            self.__lock__.release()


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()
        self._lock = allocate_lock()

    def __release_local__(self):
        self._local.__release_local__()

    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"""
        self._lock.acquire()
        try:
            rv = getattr(self._local, 'stack', None)
            if rv is None:
                self._local.stack = rv = []
            rv.append(obj)
            return rv
        finally:
            self._lock.release()

    def pop(self):
        """Removes the topmost item from the stack, will return the
        old value or `None` if the stack was already empty.
        """
        self._lock.acquire()
        try:
            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()
        finally:
            self._lock.release()

    @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`.  Everytime the manager cleans up
    it, will clean up all the data left in the locals for this context.

    .. versionchanged:: 0.6.1
       Instead of a manager the :func:`release_local` function can be used
       as well.
    """

    def __init__(self, locals=None):
        if locals is None:
            self.locals = []
        elif isinstance(locals, Local):
            self.locals = [locals]
        else:
            self.locals = list(locals)

    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.
        """
        return get_ident()

    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()`.
        """
        ident = self.get_ident()
        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 _patch_wrapper(func, self.make_middleware(func))

    def __repr__(self):
        return '<%s storages: %d>' % (
            self.__class__.__name__,
            len(self.locals)
        )


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 import Local
        l = Local()

        # these are proxies
        request = l('request')
        user = l('user')


        from werkzeug 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 instanciated with a callable as well now.
    """
    __slots__ = ('__local', '__dict__', '__name__')

    def __init__(self, local, name=None):
        object.__setattr__(self, '_LocalProxy__local', local)
        object.__setattr__(self, '__name__', name)

    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:
            return AttributeError('__dict__')

    def __repr__(self):
        try:
            obj = self._get_current_object()
        except RuntimeError:
            return '<%s unbound>' % self.__class__.__name__
        return repr(obj)

    def __nonzero__(self):
        try:
            return bool(self._get_current_object())
        except RuntimeError:
            return False

    def __unicode__(self):
        try:
            return unicode(self._get_current_object())
        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]

    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)
    __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()
    __getslice__ = lambda x, i, j: x._get_current_object()[i:j]
    __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())
    __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.__coerce__(x, o)
    __enter__ = lambda x: x.__enter__()
    __exit__ = lambda x, *a, **kw: x.__exit__(*a, **kw)