flask/flask/ctx.py

# -*- coding: utf-8 -*-
"""
    flask.ctx
    ~~~~~~~~~

    Implements the objects required to keep the context.

    :copyright: (c) 2010 by Armin Ronacher.
    :license: BSD, see LICENSE for more details.
"""

from werkzeug.exceptions import HTTPException

from .globals import _request_ctx_stack
from .session import _NullSession


class _RequestGlobals(object):
    pass


def has_request_context():
    """If you have code that wants to test if a request context is there or
    not this function can be used.  For instance if you want to take advantage
    of request information is it's available but fail silently if the request
    object is unavailable.

    ::

        class User(db.Model):

            def __init__(self, username, remote_addr=None):
                self.username = username
                if remote_addr is None and has_request_context():
                    remote_addr = request.remote_addr
                self.remote_addr = remote_addr

    Alternatively you can also just test any of the context bound objects
    (such as :class:`request` or :class:`g` for truthness)::

        class User(db.Model):

            def __init__(self, username, remote_addr=None):
                self.username = username
                if remote_addr is None and request:
                    remote_addr = request.remote_addr
                self.remote_addr = remote_addr

    .. versionadded:: 0.7
    """
    return _request_ctx_stack.top is not None


class _RequestContext(object):
    """The request context contains all request relevant information.  It is
    created at the beginning of the request and pushed to the
    `_request_ctx_stack` and removed at the end of it.  It will create the
    URL adapter and request object for the WSGI environment provided.
    """

    def __init__(self, app, environ):
        self.app = app
        self.request = app.request_class(environ)
        self.url_adapter = app.create_url_adapter(self.request)
        self.g = _RequestGlobals()
        self.flashes = None
        self.session = None

        try:
            url_rule, self.request.view_args = \
                self.url_adapter.match(return_rule=True)
            self.request.url_rule = url_rule
        except HTTPException, e:
            self.request.routing_exception = e

    def push(self):
        """Binds the request context."""
        _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. flask-sqlalchemy).
        self.session = self.app.open_session(self.request)
        if self.session is None:
            self.session = _NullSession()

    def pop(self):
        """Pops the request context."""
        _request_ctx_stack.pop()

    def __enter__(self):
        self.push()
        return self

    def __exit__(self, exc_type, exc_value, tb):
        # do not pop the request stack if we are in debug mode and an
        # exception happened.  This will allow the debugger to still
        # access the request object in the interactive shell.  Furthermore
        # the context can be force kept alive for the test client.
        # See flask.testing for how this works.
        if not self.request.environ.get('flask._preserve_context') and \
           (tb is None or not self.app.debug):
            self.pop()