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.. _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:
Blueprint Objects
-----------------
.. autoclass:: Blueprint
:members:
:inherited-members:
Incoming Request Data
---------------------
.. autoclass:: Request
:members:
.. attribute:: form
A :class:`~werkzeug.datastructures.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.datastructures.MultiDict` with the parsed contents of the query
string. (The part in the URL after the question mark).
.. attribute:: values
A :class:`~werkzeug.datastructures.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:: headers
The incoming request headers as a dictionary like object.
.. 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.datastructures.MultiDict` with files uploaded as part of a
`POST` or `PUT` request. Each file is stored as
:class:`~werkzeug.datastructures.FileStorage` object. It basically behaves like a
standard file object you know from Python, with the difference that
it also has a :meth:`~werkzeug.datastructures.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.
.. 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.wrappers.Request`
subclass and provides all of the attributes Werkzeug defines. This
just shows a quick overview of the most important ones.
Response Objects
----------------
.. autoclass:: flask.Response
:members: set_cookie, data, mimetype
.. attribute:: headers
A :class:`Headers` object representing the response headers.
.. attribute:: status
A string with a response status.
.. 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 they know 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.
Session Interface
-----------------
.. versionadded:: 0.8
The session interface provides a simple way to replace the session
implementation that Flask is using.
.. currentmodule:: flask.sessions
.. autoclass:: SessionInterface
:members:
.. autoclass:: SecureCookieSessionInterface
:members:
.. autoclass:: NullSession
:members:
.. autoclass:: SessionMixin
:members:
.. admonition:: Notice
The ``PERMANENT_SESSION_LIFETIME`` config key can also be an integer
starting with Flask 0.8. Either catch this down yourself or use
the :attr:`~flask.Flask.permanent_session_lifetime` attribute on the
app which converts the result to an integer automatically.
Test Client
-----------
.. currentmodule:: flask.testing
.. autoclass:: FlaskClient
:members:
Application Globals
-------------------
.. currentmodule:: flask
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:: has_request_context
.. autofunction:: url_for
.. function:: abort(code)
Raises an :exc:`~werkzeug.exceptions.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:: safe_join
.. 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
<script type=text/javascript>
doSomethingWith({{ user.username|tojson|safe }});
</script>
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:
Extensions
----------
.. data:: flask.ext
This module acts as redirect import module to Flask extensions. It was
added in 0.8 as the canonical way to import Flask extensions and makes
it possible for us to have more flexibility in how we distribute
extensions.
If you want to use an extension named “Flask-Foo” you would import it
from :data:`~flask.ext` as follows::
from flask.ext import foo
.. versionadded:: 0.8
Useful Internals
----------------
.. autoclass:: flask.ctx.RequestContext
:members:
.. data:: _request_ctx_stack
The internal :class:`~werkzeug.local.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
.. autoclass:: flask.blueprints.BlueprintSetupState
:members:
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`.
.. data:: request_tearing_down
This signal is sent when the application is tearing down the request.
This is always called, even if an error happened. No arguments are
provided.
.. 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
Class Based Views
-----------------
.. versionadded:: 0.7
.. currentmodule:: None
.. autoclass:: flask.views.View
:members:
.. autoclass:: flask.views.MethodView
:members:
.. _url-route-registrations:
URL Route Registrations
-----------------------
Generally there are three ways to define rules for the routing system:
1. You can use the :meth:`flask.Flask.route` decorator.
2. You can use the :meth:`flask.Flask.add_url_rule` function.
3. You can directly access the underlying Werkzeug routing system
which is exposed as :attr:`flask.Flask.url_map`.
Variable parts in the route can be specified with angular brackets
(``/user/<username>``). By default a variable part in the URL accepts any
string without a slash however a different converter can be specified as
well by using ``<converter:name>``.
Variable parts are passed to the view function as keyword arguments.
The following converters are available:
=========== ===============================================
`unicode` accepts any text without a slash (the default)
`int` accepts integers
`float` like `int` but for floating point values
`path` like the default but also accepts slashes
=========== ===============================================
Here are some examples::
@app.route('/')
def index():
pass
@app.route('/<username>')
def show_user(username):
pass
@app.route('/post/<int:post_id>')
def show_post(post_id):
pass
An important detail to keep in mind is how Flask deals with trailing
slashes. The idea is to keep each URL unique so the following rules
apply:
1. If a rule ends with a slash and is requested without a slash by the
user, the user is automatically redirected to the same page with a
trailing slash attached.
2. If a rule does not end with a trailing slash and the user requests the
page with a trailing slash, a 404 not found is raised.
This is consistent with how web servers deal with static files. This
also makes it possible to use relative link targets safely.
You can also define multiple rules for the same function. They have to be
unique however. Defaults can also be specified. Here for example is a
definition for a URL that accepts an optional page::
@app.route('/users/', defaults={'page': 1})
@app.route('/users/page/<int:page>')
def show_users(page):
pass
This specifies that ``/users/`` will be the URL for page one and
``/users/page/N`` will be the URL for page `N`.
Here are the parameters that :meth:`~flask.Flask.route` and
:meth:`~flask.Flask.add_url_rule` accept. The only difference is that
with the route parameter the view function is defined with the decorator
instead of the `view_func` parameter.
=============== ==========================================================
`rule` the URL roule as string
`endpoint` the endpoint for the registered URL rule. Flask itself
assumes that the name of the view function is the name
of the endpoint if not explicitly stated.
`view_func` the function to call when serving a request to the
provided endpoint. If this is not provided one can
specify the function later by storing it in the
:attr:`~flask.Flask.view_functions` dictionary with the
endpoint as key.
`defaults` A dictionary with defaults for this rule. See the
example above for how defaults work.
`subdomain` specifies the rule for the subdomain in case subdomain
matching is in use. If not specified the default
subdomain is assumed.
`**options` the options to be forwarded to the underlying
:class:`~werkzeug.routing.Rule` object. A change to
Werkzeug is handling of method options. methods is a list
of methods this rule should be limited to (`GET`, `POST`
etc.). By default a rule just listens for `GET` (and
implicitly `HEAD`). Starting with Flask 0.6, `OPTIONS` is
implicitly added and handled by the standard request
handling. They have to be specified as keyword arguments.
=============== ==========================================================
.. _view-func-options:
View Function Options
---------------------
For internal usage the view functions can have some attributes attached to
customize behavior the view function would normally not have control over.
The following attributes can be provided optionally to either override
some defaults to :meth:`~flask.Flask.add_url_rule` or general behavior:
- `__name__`: The name of a function is by default used as endpoint. If
endpoint is provided explicitly this value is used. Additionally this
will be prefixed with the name of the blueprint by default which
cannot be customized from the function itself.
- `methods`: If methods are not provided when the URL rule is added,
Flask will look on the view function object itself is an `methods`
attribute exists. If it does, it will pull the information for the
methods from there.
- `provide_automatic_options`: if this attribute is set Flask will
either force enable or disable the automatic implementation of the
HTTP `OPTIONS` response. This can be useful when working with
decorators that want to customize the `OPTIONS` response on a per-view
basis.
Full example::
def index():
if request.method == 'OPTIONS':
# custom options handling here
...
return 'Hello World!'
index.provide_automatic_options = False
index.methods = ['GET', 'OPTIONS']
app.add_url_rule('/', index)
.. versionadded:: 0.8
The `provide_automatic_options` functionality was added.