.. _api: API === .. module:: flask This part of the documentation covers all the interfaces of Flask. For parts where Flask depends on external libraries, we document the most important right here and provide links to the canonical documentation. Application Object ------------------ .. autoclass:: Flask :members: :inherited-members: Module Objects -------------- .. autoclass:: Module :members: :inherited-members: Incoming Request Data --------------------- .. autoclass:: Request .. class:: request To access incoming request data, you can use the global `request` object. Flask parses incoming request data for you and gives you access to it through that global object. Internally Flask makes sure that you always get the correct data for the active thread if you are in a multithreaded environment. This is a proxy. See :ref:`notes-on-proxies` for more information. The request object is an instance of a :class:`~werkzeug.Request` subclass and provides all of the attributes Werkzeug defines. This just shows a quick overview of the most important ones. .. attribute:: form A :class:`~werkzeug.MultiDict` with the parsed form data from `POST` or `PUT` requests. Please keep in mind that file uploads will not end up here, but instead in the :attr:`files` attribute. .. attribute:: args A :class:`~werkzeug.MultiDict` with the parsed contents of the query string. (The part in the URL after the question mark). .. attribute:: values A :class:`~werkzeug.CombinedMultiDict` with the contents of both :attr:`form` and :attr:`args`. .. attribute:: cookies A :class:`dict` with the contents of all cookies transmitted with the request. .. attribute:: stream If the incoming form data was not encoded with a known mimetype the data is stored unmodified in this stream for consumption. Most of the time it is a better idea to use :attr:`data` which will give you that data as a string. The stream only returns the data once. .. attribute:: data Contains the incoming request data as string in case it came with a mimetype Flask does not handle. .. attribute:: files A :class:`~werkzeug.MultiDict` with files uploaded as part of a `POST` or `PUT` request. Each file is stored as :class:`~werkzeug.FileStorage` object. It basically behaves like a standard file object you know from Python, with the difference that it also has a :meth:`~werkzeug.FileStorage.save` function that can store the file on the filesystem. .. attribute:: environ The underlying WSGI environment. .. attribute:: method The current request method (``POST``, ``GET`` etc.) .. attribute:: path .. attribute:: script_root .. attribute:: url .. attribute:: base_url .. attribute:: url_root Provides different ways to look at the current URL. Imagine your application is listening on the following URL:: http://www.example.com/myapplication And a user requests the following URL:: http://www.example.com/myapplication/page.html?x=y In this case the values of the above mentioned attributes would be the following: ============= ====================================================== `path` ``/page.html`` `script_root` ``/myapplication`` `base_url` ``http://www.example.com/myapplication/page.html`` `url` ``http://www.example.com/myapplication/page.html?x=y`` `url_root` ``http://www.example.com/myapplication/`` ============= ====================================================== .. attribute:: is_xhr `True` if the request was triggered via a JavaScript `XMLHttpRequest`. This only works with libraries that support the ``X-Requested-With`` header and set it to `XMLHttpRequest`. Libraries that do that are prototype, jQuery and Mochikit and probably some more. .. attribute:: json Contains the parsed body of the JSON request if the mimetype of the incoming data was `application/json`. This requires Python 2.6 or an installed version of simplejson. Response Objects ---------------- .. autoclass:: flask.Response :members: set_cookie, data, mimetype .. attribute:: headers A :class:`Headers` object representing the response headers. .. attribute:: status_code The response status as integer. Sessions -------- If you have the :attr:`Flask.secret_key` set you can use sessions in Flask applications. A session basically makes it possible to remember information from one request to another. The way Flask does this is by using a signed cookie. So the user can look at the session contents, but not modify it unless he knows the secret key, so make sure to set that to something complex and unguessable. To access the current session you can use the :class:`session` object: .. class:: session The session object works pretty much like an ordinary dict, with the difference that it keeps track on modifications. This is a proxy. See :ref:`notes-on-proxies` for more information. The following attributes are interesting: .. attribute:: new `True` if the session is new, `False` otherwise. .. attribute:: modified `True` if the session object detected a modification. Be advised that modifications on mutable structures are not picked up automatically, in that situation you have to explicitly set the attribute to `True` yourself. Here an example:: # this change is not picked up because a mutable object (here # a list) is changed. session['objects'].append(42) # so mark it as modified yourself session.modified = True .. attribute:: permanent If set to `True` the session lives for :attr:`~flask.Flask.permanent_session_lifetime` seconds. The default is 31 days. If set to `False` (which is the default) the session will be deleted when the user closes the browser. Application Globals ------------------- To share data that is valid for one request only from one function to another, a global variable is not good enough because it would break in threaded environments. Flask provides you with a special object that ensures it is only valid for the active request and that will return different values for each request. In a nutshell: it does the right thing, like it does for :class:`request` and :class:`session`. .. data:: g Just store on this whatever you want. For example a database connection or the user that is currently logged in. This is a proxy. See :ref:`notes-on-proxies` for more information. Useful Functions and Classes ---------------------------- .. data:: current_app Points to the application handling the request. This is useful for extensions that want to support multiple applications running side by side. This is a proxy. See :ref:`notes-on-proxies` for more information. .. autofunction:: url_for .. function:: abort(code) Raises an :exc:`~werkzeug.exception.HTTPException` for the given status code. For example to abort request handling with a page not found exception, you would call ``abort(404)``. :param code: the HTTP error code. .. autofunction:: redirect .. autofunction:: make_response .. autofunction:: send_file .. autofunction:: send_from_directory .. autofunction:: escape .. autoclass:: Markup :members: escape, unescape, striptags Message Flashing ---------------- .. autofunction:: flash .. autofunction:: get_flashed_messages Returning JSON -------------- .. autofunction:: jsonify .. data:: json If JSON support is picked up, this will be the module that Flask is using to parse and serialize JSON. So instead of doing this yourself:: try: import simplejson as json except ImportError: import json You can instead just do this:: from flask import json For usage examples, read the :mod:`json` documentation. The :func:`~json.dumps` function of this json module is also available as filter called ``|tojson`` in Jinja2. Note that inside `script` tags no escaping must take place, so make sure to disable escaping with ``|safe`` if you intend to use it inside `script` tags: .. sourcecode:: html+jinja Note that the ``|tojson`` filter escapes forward slashes properly. Template Rendering ------------------ .. autofunction:: render_template .. autofunction:: render_template_string .. autofunction:: get_template_attribute Configuration ------------- .. autoclass:: Config :members: Useful Internals ---------------- .. data:: _request_ctx_stack The internal :class:`~werkzeug.LocalStack` that is used to implement all the context local objects used in Flask. This is a documented instance and can be used by extensions and application code but the use is discouraged in general. The following attributes are always present on each layer of the stack: `app` the active Flask application. `url_adapter` the URL adapter that was used to match the request. `request` the current request object. `session` the active session object. `g` an object with all the attributes of the :data:`flask.g` object. `flashes` an internal cache for the flashed messages. Example usage:: from flask import _request_ctx_stack def get_session(): ctx = _request_ctx_stack.top if ctx is not None: return ctx.session .. versionchanged:: 0.4 The request context is automatically popped at the end of the request for you. In debug mode the request context is kept around if exceptions happen so that interactive debuggers have a chance to introspect the data. With 0.4 this can also be forced for requests that did not fail and outside of `DEBUG` mode. By setting ``'flask._preserve_context'`` to `True` on the WSGI environment the context will not pop itself at the end of the request. This is used by the :meth:`~flask.Flask.test_client` for example to implement the deferred cleanup functionality. You might find this helpful for unittests where you need the information from the context local around for a little longer. Make sure to properly :meth:`~werkzeug.LocalStack.pop` the stack yourself in that situation, otherwise your unittests will leak memory. Signals ------- .. when modifying this list, also update the one in signals.rst .. versionadded:: 0.6 .. data:: signals_available `True` if the signalling system is available. This is the case when `blinker`_ is installed. .. data:: template_rendered This signal is sent when a template was successfully rendered. The signal is invoked with the instance of the template as `template` and the context as dictionary (named `context`). .. data:: request_started This signal is sent before any request processing started but when the request context was set up. Because the request context is already bound, the subscriber can access the request with the standard global proxies such as :class:`~flask.request`. .. data:: request_finished This signal is sent right before the response is sent to the client. It is passed the response to be sent named `response`. .. data:: got_request_exception This signal is sent when an exception happens during request processing. It is sent *before* the standard exception handling kicks in and even in debug mode, where no exception handling happens. The exception itself is passed to the subscriber as `exception`. .. currentmodule:: None .. class:: flask.signals.Namespace An alias for :class:`blinker.base.Namespace` if blinker is available, otherwise a dummy class that creates fake signals. This class is available for Flask extensions that want to provide the same fallback system as Flask itself. .. method:: signal(name, doc=None) Creates a new signal for this namespace if blinker is available, otherwise returns a fake signal that has a send method that will do nothing but will fail with a :exc:`RuntimeError` for all other operations, including connecting. .. _blinker: http://pypi.python.org/pypi/blinker .. _notes-on-proxies: Notes On Proxies ---------------- Some of the objects provided by Flask are proxies to other objects. The reason behind this is that these proxies are shared between threads and they have to dispatch to the actual object bound to a thread behind the scenes as necessary. Most of the time you don't have to care about that, but there are some exceptions where it is good to know that this object is an actual proxy: - The proxy objects do not fake their inherited types, so if you want to perform actual instance checks, you have to do that on the instance that is being proxied (see `_get_current_object` below). - if the object reference is important (so for example for sending :ref:`signals`) If you need to get access to the underlying object that is proxied, you can use the :meth:`~werkzeug.LocalProxy._get_current_object` method:: app = current_app._get_current_object() my_signal.send(app)