.. 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:: Module :members: :inherited-members:
.. autoclass:: 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.
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.
.. 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.
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:
The session object works pretty much like an ordinary dict, with the difference that it keeps track on modifications.
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 life 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.
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.
.. 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.
.. 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
.. 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:: _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.