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@ -3,7 +3,7 @@
Quickstart Quickstart
========== ==========
Eager to get started? This page gives a good introduction in how to gets Eager to get started? This page gives a good introduction in how to get
started with Flask. This assumes you already have Flask installed. If started with Flask. This assumes you already have Flask installed. If
you do not, head over to the :ref:`installation` section. you do not, head over to the :ref:`installation` section.
@ -37,14 +37,14 @@ see your hello world greeting.
So what did that code do? So what did that code do?
1. first we imported the :class:`~flask.Flask` class. An instance of this 1. First we imported the :class:`~flask.Flask` class. An instance of this
class will be our WSGI application. The first argument is the name of class will be our WSGI application. The first argument is the name of
the application's module. If you are using a single module (like here) the application's module. If you are using a single module (like here)
you should use `__name__` because depending on if it's started as you should use `__name__` because depending on if it's started as
application or imported as module the name will be different application or imported as module the name will be different
(``'__main__'`` versus the actual import name). For more information (``'__main__'`` versus the actual import name). For more information
on that, have a look at the :class:`~flask.Flask` documentation. on that, have a look at the :class:`~flask.Flask` documentation.
2. next we create an instance of it. We pass it the name of the module / 2. Next we create an instance of it. We pass it the name of the module /
package. This is needed so that Flask knows where it should look for package. This is needed so that Flask knows where it should look for
templates, static files and so on. templates, static files and so on.
3. Then we use the :meth:`~flask.Flask.route` decorator to tell Flask 3. Then we use the :meth:`~flask.Flask.route` decorator to tell Flask
@ -81,7 +81,7 @@ To stop the server, hit control-C.
Debug Mode Debug Mode
---------- ----------
Now that :meth:`~flask.Flask.run` method is nice to start a local The :meth:`~flask.Flask.run` method is nice to start a local
development server, but you would have to restart it manually after each development server, but you would have to restart it manually after each
change you do to code. That is not very nice and Flask can do better. If change you do to code. That is not very nice and Flask can do better. If
you enable the debug support the server will reload itself on code changes you enable the debug support the server will reload itself on code changes
@ -101,11 +101,10 @@ Both will have exactly the same effect.
.. admonition:: Attention .. admonition:: Attention
The interactive debugger however does not work in forking environments Even though the interactive debugger does not work in forking environments
which makes it nearly impossible to use on production servers but the (which makes it nearly impossible to use on production servers), it still
debugger still allows the execution of arbitrary code which makes it a allows the execution of arbitrary code. That makes it a major security
major security risk and **must never be used on production machines** risk and therefore it **must never be used on production machines**.
because of that.
Screenshot of the debugger in action: Screenshot of the debugger in action:
@ -118,11 +117,14 @@ Screenshot of the debugger in action:
Routing Routing
------- -------
As you have seen above, the :meth:`~flask.Flask.route` decorator is used Modern web applications have beautiful URLs. This helps people remember
to bind a function to a URL. But there is more to it! You can make the URLs which is especially handy for applications that are used from
certain parts of the URL dynamic and attach multiple rules to a function. mobile devices with slower network connections. If the user can directly
go to the desired page without having to hit the index page it is more
likely he will like the page and come back next time.
Here some examples:: As you have seen above, the :meth:`~flask.Flask.route` decorator is used
to bind a function to a URL. Here are some basic examples::
@app.route('/') @app.route('/')
def index(): def index():
@ -132,20 +134,16 @@ Here some examples::
def hello(): def hello():
return 'Hello World' return 'Hello World'
But there is more to it! You can make certain parts of the URL dynamic
and attach multiple rules to a function.
Variable Rules Variable Rules
`````````````` ``````````````
Modern web applications have beautiful URLs. This helps people remember
the URLs which is especially handy for applications that are used from
mobile devices with slower network connections. If the user can directly
go to the desired page without having to hit the index page it is more
likely he will like the page and come back next time.
To add variable parts to a URL you can mark these special sections as To add variable parts to a URL you can mark these special sections as
``<variable_name>``. Such a part is then passed as keyword argument to ``<variable_name>``. Such a part is then passed as keyword argument to
your function. Optionally a converter can be specified by specifying a your function. Optionally a converter can be specified by specifying a
rule with ``<converter:variable_name>``. Here some nice examples:: rule with ``<converter:variable_name>``. Here are some nice examples::
@app.route('/user/<username>') @app.route('/user/<username>')
def show_user_profile(username): def show_user_profile(username):
@ -203,12 +201,12 @@ The following converters exist:
URL Building URL Building
```````````` ````````````
If it can match URLs, can it also generate them? Of course you can. To If it can match URLs, can it also generate them? Of course it can. To
build a URL to a specific function you can use the :func:`~flask.url_for` build a URL to a specific function you can use the :func:`~flask.url_for`
function. It accepts the name of the function as first argument and a function. It accepts the name of the function as first argument and a
number of keyword arguments, each corresponding to the variable part of number of keyword arguments, each corresponding to the variable part of
the URL rule. Unknown variable parts are appended to the URL as query the URL rule. Unknown variable parts are appended to the URL as query
parameter. Here some examples: parameter. Here are some examples:
>>> from flask import Flask, url_for >>> from flask import Flask, url_for
>>> app = Flask(__name__) >>> app = Flask(__name__)
@ -256,7 +254,7 @@ HTTP Methods
HTTP (the protocol web applications are speaking) knows different methods HTTP (the protocol web applications are speaking) knows different methods
to access URLs. By default a route only answers to `GET` requests, but to access URLs. By default a route only answers to `GET` requests, but
that can be changed by providing the `methods` argument to the that can be changed by providing the `methods` argument to the
:meth:`~flask.Flask.route` decorator. Here some examples:: :meth:`~flask.Flask.route` decorator. Here are some examples::
@app.route('/login', methods=['GET', 'POST']) @app.route('/login', methods=['GET', 'POST'])
def login(): def login():
@ -272,25 +270,24 @@ protocol) demands, so you can completely ignore that part of the HTTP
specification. Likewise as of Flask 0.6, `OPTIONS` is implemented for you specification. Likewise as of Flask 0.6, `OPTIONS` is implemented for you
as well automatically. as well automatically.
You have no idea what an HTTP method is? Worry not, here quick You have no idea what an HTTP method is? Worry not, here is a quick
introduction in HTTP methods and why they matter: introduction to HTTP methods and why they matter:
The HTTP method (also often called "the verb") tells the server what the The HTTP method (also often called "the verb") tells the server what the
clients wants to *do* with the requested page. The following methods are clients wants to *do* with the requested page. The following methods are
very common: very common:
`GET` `GET`
The Browser tells the server: just *get* me the information stored on The browser tells the server to just *get* the information stored on
that page and send them to me. This is probably the most common that page and send it. This is probably the most common method.
method.
`HEAD` `HEAD`
The Browser tells the server: get me the information, but I am only The browser tells the server to get the information, but it is only
interested in the *headers*, not the content of the page. An interested in the *headers*, not the content of the page. An
application is supposed to handle that as if a `GET` request was application is supposed to handle that as if a `GET` request was
received but not deliver the actual contents. In Flask you don't have received but to not deliver the actual content. In Flask you don't
to deal with that at all, the underlying Werkzeug library handles that have to deal with that at all, the underlying Werkzeug library handles
for you. that for you.
`POST` `POST`
The browser tells the server that it wants to *post* some new The browser tells the server that it wants to *post* some new
@ -301,27 +298,27 @@ very common:
`PUT` `PUT`
Similar to `POST` but the server might trigger the store procedure Similar to `POST` but the server might trigger the store procedure
multiple times by overwriting the old values more than once. Now you multiple times by overwriting the old values more than once. Now you
might be asking why this is any useful, but there are some good might be asking why is this useful, but there are some good reasons
reasons to do that. Consider the connection is lost during to do it this way. Consider that the connection gets lost during
transmission, in that situation a system between the browser and the transmission: in this situation a system between the browser and the
server might sent the request safely a second time without breaking server might receive the request safely a second time without breaking
things. With `POST` that would not be possible because it must only things. With `POST` that would not be possible because it must only
be triggered once. be triggered once.
`DELETE` `DELETE`
Remove the information that the given location. Remove the information at the given location.
`OPTIONS` `OPTIONS`
Provides a quick way for a requesting client to figure out which Provides a quick way for a client to figure out which methods are
methods are supported by this URL. Starting with Flask 0.6, this supported by this URL. Starting with Flask 0.6, this is implemented
is implemented for you automatically. for you automatically.
Now the interesting part is that in HTML4 and XHTML1, the only methods a Now the interesting part is that in HTML4 and XHTML1, the only methods a
form might submit to the server are `GET` and `POST`. But with JavaScript form can submit to the server are `GET` and `POST`. But with JavaScript
and future HTML standards you can use other methods as well. Furthermore and future HTML standards you can use the other methods as well. Furthermore
HTTP became quite popular lately and there are more things than browsers HTTP has become quite popular lately and browsers are no longer the only
that are speaking HTTP. (Your revision control system for instance might clients that are using HTTP. For instance, many revision control system
speak HTTP) use it.
.. _HTTP RFC: http://www.ietf.org/rfc/rfc2068.txt .. _HTTP RFC: http://www.ietf.org/rfc/rfc2068.txt
@ -383,7 +380,7 @@ to the :ref:`templating` section of the documentation or the official
`Jinja2 Template Documentation `Jinja2 Template Documentation
<http://jinja.pocoo.org/2/documentation/templates>`_ for more information. <http://jinja.pocoo.org/2/documentation/templates>`_ for more information.
Here an example template: Here is an example template:
.. sourcecode:: html+jinja .. sourcecode:: html+jinja
@ -411,7 +408,7 @@ markup to HTML) you can mark it as safe by using the
:class:`~jinja2.Markup` class or by using the ``|safe`` filter in the :class:`~jinja2.Markup` class or by using the ``|safe`` filter in the
template. Head over to the Jinja 2 documentation for more examples. template. Head over to the Jinja 2 documentation for more examples.
Here a basic introduction in how the :class:`~jinja2.Markup` class works: Here is a basic introduction to how the :class:`~jinja2.Markup` class works:
>>> from flask import Markup >>> from flask import Markup
>>> Markup('<strong>Hello %s!</strong>') % '<blink>hacker</blink>' >>> Markup('<strong>Hello %s!</strong>') % '<blink>hacker</blink>'
@ -425,12 +422,12 @@ u'Marked up \xbb HTML'
Autoescaping is no longer enabled for all templates. The following Autoescaping is no longer enabled for all templates. The following
extensions for templates trigger autoescaping: ``.html``, ``.htm``, extensions for templates trigger autoescaping: ``.html``, ``.htm``,
``.xml``, ``.xhtml``. Templates loaded from string will have ``.xml``, ``.xhtml``. Templates loaded from a string will have
autoescaping disabled. autoescaping disabled.
.. [#] Unsure what that :class:`~flask.g` object is? It's something you .. [#] Unsure what that :class:`~flask.g` object is? It's something in which
can store information on yourself, check the documentation of that you can store information for your own needs, check the documentation of
object (:class:`~flask.g`) and the :ref:`sqlite3` for more that object (:class:`~flask.g`) and the :ref:`sqlite3` for more
information. information.
@ -454,10 +451,9 @@ Context Locals
If you want to understand how that works and how you can implement If you want to understand how that works and how you can implement
tests with context locals, read this section, otherwise just skip it. tests with context locals, read this section, otherwise just skip it.
Certain objects in Flask are global objects, but not just a standard Certain objects in Flask are global objects, but not of the usual kind.
global object, but actually a proxy to an object that is local to a These objects are actually proxies to objects that are local to a specific
specific context. What a mouthful. But that is actually quite easy to context. What a mouthful. But that is actually quite easy to understand.
understand.
Imagine the context being the handling thread. A request comes in and the Imagine the context being the handling thread. A request comes in and the
webserver decides to spawn a new thread (or something else, the webserver decides to spawn a new thread (or something else, the
@ -469,13 +465,13 @@ It does that in an intelligent way that one application can invoke another
application without breaking. application without breaking.
So what does this mean to you? Basically you can completely ignore that So what does this mean to you? Basically you can completely ignore that
this is the case unless you are unittesting or something different. You this is the case unless you are doing something like unittesting. You
will notice that code that depends on a request object will suddenly break will notice that code that depends on a request object will suddenly break
because there is no request object. The solution is creating a request because there is no request object. The solution is creating a request
object yourself and binding it to the context. The easiest solution for object yourself and binding it to the context. The easiest solution for
unittesting is by using the :meth:`~flask.Flask.test_request_context` unittesting is by using the :meth:`~flask.Flask.test_request_context`
context manager. In combination with the `with` statement it will bind a context manager. In combination with the `with` statement it will bind a
test request so that you can interact with it. Here an example:: test request so that you can interact with it. Here is an example::
from flask import request from flask import request
@ -497,8 +493,8 @@ The Request Object
`````````````````` ``````````````````
The request object is documented in the API section and we will not cover The request object is documented in the API section and we will not cover
it here in detail (see :class:`~flask.request`), but just mention some of it here in detail (see :class:`~flask.request`). Here is a broad overview of
the most common operations. First of all you have to import it from the some of the most common operations. First of all you have to import it from
the `flask` module:: the `flask` module::
from flask import request from flask import request
@ -506,7 +502,7 @@ the `flask` module::
The current request method is available by using the The current request method is available by using the
:attr:`~flask.request.method` attribute. To access form data (data :attr:`~flask.request.method` attribute. To access form data (data
transmitted in a `POST` or `PUT` request) you can use the transmitted in a `POST` or `PUT` request) you can use the
:attr:`~flask.request.form` attribute. Here a full example of the two :attr:`~flask.request.form` attribute. Here is a full example of the two
attributes mentioned above:: attributes mentioned above::
@app.route('/login', methods=['POST', 'GET']) @app.route('/login', methods=['POST', 'GET'])
@ -534,19 +530,18 @@ To access parameters submitted in the URL (``?key=value``) you can use the
We recommend accessing URL parameters with `get` or by catching the We recommend accessing URL parameters with `get` or by catching the
`KeyError` because users might change the URL and presenting them a 400 `KeyError` because users might change the URL and presenting them a 400
bad request page in that case is a bit user unfriendly. bad request page in that case is not user friendly.
For a full list of methods and attributes on that object, head over to the For a full list of methods and attributes of the request object, head over
:class:`~flask.request` documentation. to the :class:`~flask.request` documentation.
File Uploads File Uploads
```````````` ````````````
Obviously you can handle uploaded files with Flask just as easy. Just You can handle uploaded files with Flask easily. Just make sure not to
make sure not to forget to set the ``enctype="multipart/form-data"`` forget to set the ``enctype="multipart/form-data"`` attribute on your HTML
attribute on your HTML form, otherwise the browser will not transmit your form, otherwise the browser will not transmit your files at all.
files at all.
Uploaded files are stored in memory or at a temporary location on the Uploaded files are stored in memory or at a temporary location on the
filesystem. You can access those files by looking at the filesystem. You can access those files by looking at the
@ -554,8 +549,8 @@ filesystem. You can access those files by looking at the
uploaded file is stored in that dictionary. It behaves just like a uploaded file is stored in that dictionary. It behaves just like a
standard Python :class:`file` object, but it also has a standard Python :class:`file` object, but it also has a
:meth:`~werkzeug.FileStorage.save` method that allows you to store that :meth:`~werkzeug.FileStorage.save` method that allows you to store that
file on the filesystem of the server. Here a simple example how that file on the filesystem of the server. Here is a simple example showing how
works:: that works::
from flask import request from flask import request
@ -600,8 +595,8 @@ Redirects and Errors
-------------------- --------------------
To redirect a user to somewhere else you can use the To redirect a user to somewhere else you can use the
:func:`~flask.redirect` function, to abort a request early with an error :func:`~flask.redirect` function. To abort a request early with an error
code the :func:`~flask.abort` function. Here an example how this works:: code use the :func:`~flask.abort` function. Here an example how this works::
from flask import abort, redirect, url_for from flask import abort, redirect, url_for
@ -681,7 +676,7 @@ sessions work::
The here mentioned :func:`~flask.escape` does escaping for you if you are The here mentioned :func:`~flask.escape` does escaping for you if you are
not using the template engine (like in this example). not using the template engine (like in this example).
.. admonition:: How to generate good Secret Keys .. admonition:: How to generate good secret keys
The problem with random is that it's hard to judge what random is. And The problem with random is that it's hard to judge what random is. And
a secret key should be as random as possible. Your operating system a secret key should be as random as possible. Your operating system
@ -715,16 +710,17 @@ Logging
.. versionadded:: 0.3 .. versionadded:: 0.3
Sometimes you might be in the situation where you deal with data that Sometimes you might be in a situation where you deal with data that
should be correct, but actually is not. For example you have some client should be correct, but actually is not. For example you may have some client
side code that sends an HTTP request to the server, and it's obviously side code that sends an HTTP request to the server but it's obviously
malformed. This might be caused by a user tempering with the data, or the malformed. This might be caused by a user tempering with the data, or the
client code failed. Most the time, it's okay to reply with ``400 Bad client code failing. Most of the time, it's okay to reply with ``400 Bad
Request`` in that situation, but other times it is not and the code has to Request`` in that situation, but sometimes that won't do and the code has
continue working. to continue working.
Yet you want to log that something fishy happened. This is where loggers You may still want to log that something fishy happened. This is where
come in handy. As of Flask 0.3 a logger is preconfigured for you to use. loggers come in handy. As of Flask 0.3 a logger is preconfigured for you
to use.
Here are some example log calls:: Here are some example log calls::
@ -733,8 +729,9 @@ Here are some example log calls::
app.logger.error('An error occurred') app.logger.error('An error occurred')
The attached :attr:`~flask.Flask.logger` is a standard logging The attached :attr:`~flask.Flask.logger` is a standard logging
:class:`~logging.Logger`, so head over to the official stdlib :class:`~logging.Logger`, so head over to the official `logging
documentation for more information. documentation <http://docs.python.org/library/logging.html>`_ for more
information.
Hooking in WSGI Middlewares Hooking in WSGI Middlewares
--------------------------- ---------------------------