.. 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.
.. autoclass:: Flask :members: :inherited-members:
.. autoclass:: Blueprint :members: :inherited-members:
.. 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.
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.
.. 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.
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:
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.
.. 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:
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.
.. currentmodule:: flask.testing
.. autoclass:: FlaskClient :members:
.. 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.
.. 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
.. autofunction:: flash
.. autofunction:: get_flashed_messages
.. 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.
.. autofunction:: render_template
.. autofunction:: render_template_string
.. autofunction:: get_template_attribute
.. autoclass:: Config :members:
.. 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
.. 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:
.. 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
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.
.. versionadded:: 0.7
.. currentmodule:: None
.. autoclass:: flask.views.View :members:
.. autoclass:: flask.views.MethodView :members:
Generally there are three ways to define rules for the routing system:
- You can use the :meth:`flask.Flask.route` decorator.
- You can use the :meth:`flask.Flask.add_url_rule` function.
- 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:
- 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.
- 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. |
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.