Edited the entire section for clarity and concision. I rewrote sentences
to make them shorter and to reduce ambiguity.
Added a code sample to show the path converter type
Removed the HTTP method overview. Although it was well written, the
overview wasn't necessary in the quickstart. Readers can easily find an
overview elsewhere.
@ -159,14 +159,9 @@ Have another debugger in mind? See :ref:`working-with-debuggers`.
Routing
-------
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 they will like the page and come back next time.
Modern web applications use meaningful URLs to help users. Users are more likely to like a page and come back if the page uses a meaningful URL they can remember and use to directly visit a page.
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::
As you saw in the minimal application, you can use the :meth:`~flask.Flask.route` decorator to bind a function to a meaningful URL. For example::
@app.route('/')
def index():
@ -176,16 +171,12 @@ bind a function to a URL. Here are some basic examples::
def hello():
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.
You can do more! You can make parts of the URL dynamic and attach multiple rules to a function.
Variable Rules
``````````````
To add variable parts to a URL you can mark these special sections as
``<variable_name>``. Such a part is then passed as a keyword argument to your
function. Optionally a converter can be used by specifying a rule with
``<converter:variable_name>``. Here are some nice examples::
You can add variable sections to a URL by marking sections with ``<variable_name>``. Your function then receives the ``<variable_name>`` as a keyword argument. Optionally, you can use a converter to specify a rule with ``<converter:variable_name>``. For example::
@app.route('/user/<username>')
def show_user_profile(username):
@ -197,22 +188,25 @@ function. Optionally a converter can be used by specifying a rule with
# show the post with the given id, the id is an integer
Flask's URL rules are based on Werkzeug's routing module. The idea
behind that module is to ensure beautiful and unique URLs based on
precedents laid down by Apache and earlier HTTP servers.
Flask's URL rules are based on Werkzeug's routing module. The routing module creates meaningful and unique URLs based on precedents laid down by Apache and earlier HTTP servers.
Take these two rules::
@ -224,15 +218,9 @@ The following converters exist:
def about():
return 'The about page'
Though they look rather similar, they differ in their use of the trailing
slash in the URL *definition*. In the first case, the canonical URL for the
``projects`` endpoint has a trailing slash. In that sense, it is similar to
a folder on a filesystem. Accessing it without a trailing slash will cause
Flask to redirect to the canonical URL with the trailing slash.
Though they look similar, they differ in their use of the trailing slash in the URL *definition*. In the first case, the canonical URL for the ``projects`` endpoint uses a trailing slash. It's similar to a folder in a file system, and if you access the URL without a trailing slash, Flask redirects you to the canonical URL with the trailing slash.
In the second case, however, the URL is defined without a trailing slash,
rather like the pathname of a file on UNIX-like systems. Accessing the URL
with a trailing slash will produce a 404 "Not Found" error.
In the second case, however, the URL definition lacks a trailing slash like the pathname of a file on UNIX-like systems. Accessing the URL with a trailing slash produces a 404 “Not Found” error.
This behavior allows relative URLs to continue working even if the trailing
slash is omitted, consistent with how Apache and other servers work. Also,
@ -245,12 +233,19 @@ The following converters exist:
URL Building
````````````
If it can match URLs, can Flask also generate them? Of course it can. To
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 number
of keyword arguments, each corresponding to the variable part of the URL rule.
Unknown variable parts are appended to the URL as query parameters. Here are
some examples::
Flask can match URLs, but can it also generate them? Yes! To build a URL to a specific function, you can use the :func:`~flask.url_for` function. It accepts the name of the function as its first argument and any number of keyword arguments, each corresponding to a variable part of the URL rule. Unknown variable parts are appended to the URL as query parameters.
Why would you want to build URLs using the URL reversing function
:func:`~flask.url_for` instead of hard-coding them into your templates? Three good reasons:
1. Reversing is often more descriptive than hard-coding the URLs. More importantly, you can change your URLs in one go instead of needing to remember to manually change hard-coded URLs.
2. URL building handles escaping of special characters and Unicode data transparently.
3. If your application is placed outside the URL root, for example, in ``/myapplication`` instead of ``/``, :func:`~flask.url_for` properly handles that for you.
For example, here we use the :meth:`~flask.Flask.test_request_context` method to try out :func:`~flask.url_for`. :meth:`~flask.Flask.test_request_context` tells Flask to behave as though it's handling a request even while we use a Python shell. Also see, :ref:`context-locals`.
Example::
>>> from flask import Flask, url_for
>>> app = Flask(__name__)
@ -274,98 +269,19 @@ some examples::
/login?next=/
/user/John%20Doe
(This also uses the :meth:`~flask.Flask.test_request_context` method, explained
below. It tells Flask to behave as though it is handling a request, even
though we are interacting with it through a Python shell. Have a look at the
explanation below. :ref:`context-locals`).
Why would you want to build URLs using the URL reversing function
:func:`~flask.url_for` instead of hard-coding them into your templates?
There are three good reasons for this:
1. Reversing is often more descriptive than hard-coding the URLs. More
importantly, it allows you to change URLs in one go, without having to
remember to change URLs all over the place.
2. URL building will handle escaping of special characters and Unicode
data transparently for you, so you don't have to deal with them.
3. If your application is placed outside the URL root - say, in
``/myapplication`` instead of ``/`` - :func:`~flask.url_for` will handle
that properly for you.
HTTP Methods
````````````
HTTP (the protocol web applications are speaking) knows different methods for
accessing URLs. By default, a route only answers to ``GET`` requests, but that
can be changed by providing the ``methods`` argument to the
:meth:`~flask.Flask.route` decorator. Here are some examples::
from flask import request
Web application communicate using HTTP and use different methods for accessing URLs. You should familiarize yourself with the HTTP methods as you work with Flask. By default, a route only answers to ``GET`` requests. You can use the ``methods`` argument of the :meth:`~flask.Flask.route` decorator to handle different HTTP methods. For example::
@app.route('/login', methods=['GET', 'POST'])
def login():
if request.method == 'POST':
return do_the_login()
do_the_login()
else:
return show_the_login_form()
If ``GET`` is present, ``HEAD`` will be added automatically for you. You
don't have to deal with that. It will also make sure that ``HEAD`` requests
are handled as the `HTTP RFC`_ (the document describing the HTTP
protocol) demands, so you can completely ignore that part of the HTTP
specification. Likewise, as of Flask 0.6, ``OPTIONS`` is implemented for you
automatically as well.
You have no idea what an HTTP method is? Worry not, here is a quick
introduction to HTTP methods and why they matter:
The HTTP method (also often called "the verb") tells the server what the
client wants to *do* with the requested page. The following methods are
very common:
``GET``
The browser tells the server to just *get* the information stored on
that page and send it. This is probably the most common method.
``HEAD``
The browser tells the server to get the information, but it is only
interested in the *headers*, not the content of the page. An
application is supposed to handle that as if a ``GET`` request was
received but to not deliver the actual content. In Flask you don't
have to deal with that at all, the underlying Werkzeug library handles
that for you.
``POST``
The browser tells the server that it wants to *post* some new
information to that URL and that the server must ensure the data is
stored and only stored once. This is how HTML forms usually
transmit data to the server.
``PUT``
Similar to ``POST`` but the server might trigger the store procedure
multiple times by overwriting the old values more than once. Now you
might be asking why this is useful, but there are some good reasons
to do it this way. Consider that the connection is lost during
transmission: in this situation a system between the browser and the
server might receive the request safely a second time without breaking
things. With ``POST`` that would not be possible because it must only
be triggered once.
``DELETE``
Remove the information at the given location.
``OPTIONS``
Provides a quick way for a client to figure out which methods are
supported by this URL. Starting with Flask 0.6, this is implemented
for you automatically.
Now the interesting part is that in HTML4 and XHTML1, the only methods a
form can submit to the server are ``GET`` and ``POST``. But with JavaScript
and future HTML standards you can use the other methods as well. Furthermore
HTTP has become quite popular lately and browsers are no longer the only
clients that are using HTTP. For instance, many revision control systems
use it.
show_the_login_form()
If ``GET`` is present, Flask automatically adds support for the ``HEAD`` method and handles ``HEAD`` requests according to the the `HTTP RFC`_. Likewise, as of Flask 0.6, ``OPTIONS`` is automatically implemented for you.
Xephyr826
8 years ago