This tutorial introduces you to the concepts and features of the Bottle web framework. If you have questions not answered here, please check the Frequently Asked Questions page, file a ticket at the issue tracker or send an e-mail to the mailing list.
Note
This is a copy&paste from the old docs and a work in progress. Handle with care :)
A quick overview:
Bottle has no dependencies, so all you need is Python (2.5 up to 3.x should work fine) and the bottle module file. Lets start with a very basic “Hello World” example:
from bottle import route, run
@route('/hello')
def hello():
return "Hello World!"
run(host='localhost', port=8080)
Whats happening here?
This is it. Run this script, visit http://localhost:8080/hello and you will see “Hello World!” in your browser. Of cause this is a very simple example, but it shows the basic concept of how applications are built with bottle. Continue reading and you’ll see what else is possible.
The Application Object
Several functions and decorators such as route() or run() rely on a global application object to store routes, callbacks and configuration. This makes writing a small application easy, but can lead to problems in more complex scenarios. If you prefer a more explicit way to define your application and don’t mind the extra typing, you can create your own concealed application object and use that instead of the global one:
from bottle import Bottle, run
myapp = Bottle()
@myapp.route('/hello')
def hello():
return "Hello World!"
run(app=myapp, host='localhost', port=8080)
This tutorial uses the global-application syntax for the sake of simplicity. Just keep in mind that you have a choice. The object-oriented approach is further described in the tutorial-appobject section.
As you have learned before, routes are used to map URLs to callback functions. These functions are executed on every request that matches the route and their return value is returned to the browser. You can add any number of routes to a callback using the route() decorator.
from bottle import route
@route('/')
@route('/index.html')
def index():
return "<a href='/hello'>Go to Hello World page</a>"
@route('/hello')
def hello():
return "Hello World!"
As you can see, URLs and routes have nothing to do with actual files on the web server. Routes are unique names for your callbacks, nothing more and nothing less. All URLs not covered by a route are answered with a “404 Page not found” error page.
Bottle has a special syntax to add wildcards to a route and allow a single route to match a wide range of URLs. These dynamic routes are often used by blogs or wikis to create nice looking and meaningful URLs such as /archive/2010/04/21 or /wiki/Page_Title. Why? Because cool URIs don’t change. Let’s add a :name wildcard to our last example:
@route('/hello/:name')
def hello(name):
return "Hello %s!" % name
This dynamic route will match /hello/alice as well as /hello/bob. Each URL fragment covered by a wildcard is passed to the callback function as a keyword argument so you can use the information in your application.
Normal wildcards match everything up to the next slash. You can add a regular expression to change that:
@route('/object/:id#[0-9]+#')
def view_object(id):
return "Object ID: %d" % int(id)
As you can see, the keyword argument contains a string even if the wildcard is configured to only match digits. You have to explicitly cast it into an integer if you need to.
The HTTP protocol defines several request methods (sometimes referred to as “verbs”) for different tasks. GET is the default for all routes with no other method specified. These routes will match GET requests only. To handle other methods such as POST, PUT or DELETE, you may add a method keyword argument to the route() decorator or use one of the four alternative decorators: get(), post(), put() or delete().
The POST method is commonly used for HTML form submission. This example shows how to handle a login form using POST:
from bottle import get, post, request
#@route('/login')
@get('/login')
def login_form():
return '''<form method="POST">
<input name="name" type="text" />
<input name="password" type="password" />
</from>'''
#@route('/login', method='POST')
@post('/login')
def login_submit():
name = request.forms.get('name')
password = request.forms.get('password')
if check_login(name, password):
return "<p>Your login was correct</p>"
else:
return "<p>Login failed</p>"
In this example the /login URL is bound to two distinct callbacks, one for GET requests and another for POST requests. The first one displays a HTML form to the user. The second callback is invoked on a form submission and checks the login credentials the user entered into the form. The use of Request.forms is further described in the Accessing Request Data section.
Automatic Fallbacks
The special HEAD method is used to ask for the response identical to the one that would correspond to a GET request, but without the response body. This is useful for retrieving meta-information about a resource without having to download the entire document. Bottle handles these requests automatically by falling back to the corresponding GET route and cutting off the request body, if present. You don’t have to specify any HEAD routes yourself.
Additionally, the non-standard ANY method works as a low priority fallback: Routes that listen to ANY will match requests regardless of their HTTP method but only if no other more specific route is defined. This is helpful for proxy-routes that redirect requests to more specific sub-applications.
To sum it up: HEAD requests fall back to GET routes and all requests fall back to ANY routes, but only if there is no matching route for the original request method. It’s as simple as that.
Static files such as images or css files are not served automatically. You have to add a route and a callback to control which files get served and where to find them:
from bottle import static_file
@route('/static/:filename')
def server_static(filename):
return static_file(filename, root='/path/to/your/static/files')
The static_file() function is a helper to serve files in a safe and convenient way (see Static Files). This example is limited to files directly within the /path/to/your/static/files directory because the :filename wildcard won’t match a path with a slash in it. To serve files in subdirectories too, we can loosen the wildcard a bit:
@route('/static/:path#.+#')
def server_static(path):
return static_file(path, root='/path/to/your/static/files')
Be careful when specifying a relative root-path such as root='./static/files'. The working directory (./) and the project directory are not always the same.
If anything goes wrong Bottle displays an informative but fairly boring error page. You can override the default error pages using the error() decorator. It works similar to the route() decorator but expects an HTTP status code instead of a route:
@error(404)
def error404(error):
return 'Nothing here, sorry'
The error parameter passed to the error handler is an instance of HTTPError.
In pure WSGI, the range of types you may return from your application is very limited. Applications must return an iterable yielding byte strings. You may return a string (because strings are iterable) but this causes most servers to transmit your content char by char. Unicode strings are not allowed at all. This is not very practical.
Bottle is much more flexible and supports a wide range of types. It even adds a Content-Length header if possible and encodes unicode automatically, so you don’t have to. What follows is a list of data types you may return from your application callbacks and a short description of how these are handled by the framework:
The ordering of this list is significant. You may for example return a subclass of str with a read() method. It is still treated as a string instead of a file, because strings are handled first.
Changing the Default Encoding
Bottle uses the charset parameter of the Content-Type header to decide how to encode unicode strings. This header defaults to text/html; charset=UTF8 and can be changed using the Response.content_type attribute or by setting the Response.charset attribute directly. (The Response object is described in the section The Response Object.)
from bottle import response @route(‘/iso’) def get_iso():
response.charset = ‘ISO-8859-15’ return u’This will be sent with ISO-8859-15 encoding.’@route(‘/latin9’) def get_latin():
response.content_type = ‘text/html; charset=latin9’ return u’ISO-8859-15 is also known as latin9.’
In some rare cases the Python encoding names differ from the names supported by the HTTP specification. Then, you have to do both: first set the Response.content_type header (which is sent to the client unchanged) and then set the Response.charset attribute (which is used to encode unicode).
You can directly return file objects, but static_file() is the recommended way to serve static files. It automatically guesses a mime-type, adds a Last-Modified header, restricts paths to a root directory for security reasons and generates appropriate error responses (401 on permission errors, 404 on missing files). It even supports the If-Modified-Since header and eventually generates a 304 Not modified response. You can pass a custom mimetype to disable mimetype guessing.
from bottle import static_file
@route('/images/:filename#.*\.png#')
def send_image(filename):
return static_file(filename, root='/path/to/image/files', mimetype='image/png')
@route('/static/:filename')
def send_static(filename):
return static_file(filename, root='/path/to/static/files')
You can raise the return value of static_file() as an exception if you really need to.
Forced Download
Most browsers try to open downloaded files if the MIME type is known and assigned to an application (e.g. PDF files). If this is not what you want, you can force a download-dialog and even suggest a filename to the user:
@route('/download/:filename')
def download(filename):
return static_file(filename, root='/path/to/static/files', download=filename)
If the download parameter is just True, the original filename is used.
The abort() function is a shortcut for generating HTTP error pages.
from bottle import route, abort
@route('/restricted')
def restricted():
abort(401, "Sorry, access denied.")
To redirect a client to a different URL, you can send a 303 See Other response with the Location header set to the new URL. redirect() does that for you:
from bottle import redirect
@route('/wrong/url')
def wrong():
redirect("/right/url")
You may provide a different HTTP status code as a second parameter.
Note
Both functions will interrupt your callback code by raising an HTTPError exception.
Other Exceptions
All exceptions other than HTTPResponse or HTTPError will result in a 500 Internal Server Error response, so they won’t crash your WSGI server. You can turn off this behaviour to handle exceptions in your middleware by setting bottle.app().catchall to False.
Response meta-data such as the HTTP status code, response header and cookies are stored in an object called response up to the point where they are transmitted to the browser. You can manipulate these meta-data directly or use the predefined helper methods to do so. The full API and feature list is described in the API section (see Response), but the most common use cases and features are covered here, too.
Status Code
The HTTP status code controls the behaviour of the browser and defaults to 200 OK. In most scenarios you won’t need to set the Response.status attribute manually, but use the abort() helper or return an HTTPResponse instance with the appropriate status code. Any integer is allowed but only the codes defined by the HTTP specification will have an effect other than confusing the browser and breaking standards.
Response Header
Add values to the Response.headers dictionary to add or change response headers. Note that the keys are case-insensitive.
@route('/wiki/:page')
def wiki(page):
response.headers['Content-Language'] = 'en'
return get_wiki_page(page)
Bottle provides access to HTTP related meta-data such as cookies, headers and POST form data through a global request object. This object always contains information about the current request, as long as it is accessed from within a callback function. This works even in multi-threaded environments where multiple requests are handled at the same time. For details on how a global object can be thread-safe, see contextlocal.
Note
Bottle stores most of the parsed HTTP meta-data in MultiDict instances. These behave like normal dictionaries but are able to store multiple values per key. The standard dictionary access methods will only return a single value. Use the MultiDict.getall() method do receive a (possibly empty) list of all values for a specific key. The HeaderDict class inherits from MultiDict and additionally uses case insensitive keys.
The full API and feature list is described in the API section (see Request), but the most common use cases and features are covered here, too.
HTTP Header
Header are stored in Request.header. The attribute is an instance of HeaderDict which is basically a dictionary with case-insensitive keys:
from bottle import route, request
@route('/is_ajax')
def is_ajax():
if request.header.get('X-Requested-With') == 'XMLHttpRequest':
return 'This is an AJAX request'
else:
return 'This is a normal request'
Cookies
Cookies are stored in Request.COOKIES as a normal dictionary. The Request.get_cookie() method allows access to Cookies as described in a separate section. This example shows a simple cookie-based view counter:
from bottle import route, request, response
@route('/counter')
def counter():
count = int( request.COOKIES.get('counter', '0') )
count += 1
response.set_cookie('counter', str(count))
return 'You visited this page %d times' % count
Query Strings
The query string (as in /forum?id=1&page=5) is commonly used to transmit a small number of key/value pairs to the server. You can use the Request.GET dictionary to access these values and the Request.query_string attribute to get the whole string.
from bottle import route, request, response
@route('/forum')
def display_forum():
forum_id = request.GET.get('id')
page = request.GET.get('page', '1')
return 'Forum ID: %s (page %s)' % (forum_id, page)
POST Form Data and File Uploads
The request body of POST and PUT requests may contain form data encoded in various formats. Use the Request.forms attribute (a MultiDict) to access normal POST form fields. File uploads are stored separately in Request.files as cgi.FieldStorage instances. The Request.body attribute holds a file object with the raw body data.
Here is an example for a simple file upload form:
<form action="/upload" method="post" enctype="multipart/form-data">
<input type="text" name="name" />
<input type="file" name="data" />
</form>
from bottle import route, request
@route('/upload', method='POST')
def do_upload():
name = request.forms.get('name')
data = request.files.get('data')
if name and data:
raw = data.file.read() # This is dangerous for big files
filename = data.filename
return "Hello %s! Your uploaded %s (%d bytes)." % (name, filename, len(raw))
return "You missed a field."
WSGI environment
The Request object stores the WSGI environment dictionary in Request.environ and allows dict-like access to its values. See the WSGI specification for details.
@route('/my_ip')
def show_ip():
ip = request.environ.get('REMOTE_ADDR')
# or ip = request.get('REMOTE_ADDR')
# or ip = request['REMOTE_ADDR']
return "Your IP is: %s" % ip
Bottle comes with a fast and powerful built-in template engine called SimpleTemplate Engine. To render a template you can use the template() function or the view() decorator. All you have to do is to provide the name of the template and the variables you want to pass to the template as keyword arguments. Here’s a simple example of how to render a template:
@route('/hello')
@route('/hello/:name')
def hello(name='World'):
return template('hello_template', name=name)
This will load the template file hello_template.tpl and render it with the name variable set. Bottle will look for templates in the ./views/ folder or any folder specified in the bottle.TEMPLATE_PATH list.
The view() decorator allows you to return a dictionary with the template variables instead of calling template():
@route('/hello')
@route('/hello/:name')
@view('hello_template')
def hello(name='World'):
return dict(name=name)
Syntax
The template syntax is a very thin layer around the Python language. It’s main purpose is to ensure correct indentation of blocks, so you can format your template without worrying about indentation. Follow the link for a full syntax description: SimpleTemplate Engine
Here is an example template:
%if name == 'World':
<h1>Hello {{name}}!</h1>
<p>This is a test.</p>
%else:
<h1>Hello {{name.title()}}!</h1>
<p>How are you?</p>
%end
Caching
Templates are cached in memory after compilation. Modifications made to the template files will have no affect until you clear the template cache. Call bottle.TEMPLATES.clear() to do so. Caching is disabled in debug mode.
Bottle has two features that may be helpful during development.
In debug mode, bottle is much more verbose and tries to help you find bugs. You should never use debug mode in production environments.
import bottle
bottle.debug(True)
This does the following:
During development, you have to restart the server a lot to test your recent changes. The auto reloader can do this for you. Every time you edit a module file, the reloader restarts the server process and loads the newest version of your code.
from bottle import run
run(reloader=True)
How it works: the main process will not start a server, but spawn a new child process using the same command line arguments used to start the main process. All module-level code is executed at least twice! Be careful.
The child process will have os.environ['BOTTLE_CHILD'] set to True and start as a normal non-reloading app server. As soon as any of the loaded modules changes, the child process is terminated and respawned by the main process. Changes in template files will not trigger a reload. Please use debug mode to deactivate template caching.
The reloading depends on the ability to stop the child process. If you are running on Windows or any other operating system not supporting signal.SIGINT (which raises KeyboardInterrupt in Python), signal.SIGTERM is used to kill the child. Note that exit handlers and finally clauses, etc., are not executed after a SIGTERM.
Bottle uses the built-in wsgiref.SimpleServer by default. This non-threading HTTP server is perfectly fine for development and early production, but may become a performance bottleneck when server load increases.
There are three ways to eliminate this bottleneck:
The easiest way to increase performance is to install a multi-threaded and WSGI-capable HTTP server like Paste, flup, cherrypy or fapws3 and use the corresponding bottle server-adapter.
from bottle import PasteServer, FlupServer, FapwsServer, CherryPyServer
bottle.run(server=PasteServer) # Example
If bottle is missing an adapter for your favorite server or you want to tweak the server settings, you may want to manually set up your HTTP server and use bottle.default_app() to access your WSGI application.
def run_custom_paste_server(self, host, port):
myapp = bottle.default_app()
from paste import httpserver
httpserver.serve(myapp, host=host, port=port)
A single Python process can only utilise one CPU at a time, even if there are more CPU cores available. The trick is to balance the load between multiple independent Python processes to utilise all of your CPU cores.
Instead of a single Bottle application server, you start one instance of your server for each CPU core available using different local port (localhost:8080, 8081, 8082, ...). Then a high performance load balancer acts as a reverse proxy and forwards each new requests to a random Bottle processes, spreading the load between all available back end server instances. This way you can use all of your CPU cores and even spread out the load between different physical servers.
But there are a few drawbacks:
One of the fastest load balancers available is Pound but most common web servers have a proxy-module that can do the work just fine.
A call to bottle.default_app() returns your WSGI application. After applying as many WSGI middleware modules as you like, you can tell bottle.run() to use your wrapped application, instead of the default one.
from bottle import default_app, run
app = default_app()
newapp = YourMiddleware(app)
run(app=newapp)
Bottle creates a single instance of bottle.Bottle() and uses it as a default for most of the module-level decorators and the bottle.run() routine. bottle.default_app() returns (or changes) this default. You may, however, create your own instances of bottle.Bottle().
from bottle import Bottle, run
mybottle = Bottle()
@mybottle.route('/')
def index():
return 'default_app'
run(app=mybottle)
Instead of running your own HTTP server from within Bottle, you can attach Bottle applications to an Apache server using mod_wsgi and Bottle’s WSGI interface.
All you need is an app.wsgi file that provides an application object. This object is used by mod_wsgi to start your application and should be a WSGI-compatible Python callable.
File /var/www/yourapp/app.wsgi:
# Change working directory so relative paths (and template lookup) work again
os.chdir(os.path.dirname(__file__))
import bottle
# ... add or import your bottle app code here ...
# Do NOT use bottle.run() with mod_wsgi
application = bottle.default_app()
The Apache configuration may look like this:
<VirtualHost *>
ServerName example.com
WSGIDaemonProcess yourapp user=www-data group=www-data processes=1 threads=5
WSGIScriptAlias / /var/www/yourapp/app.wsgi
<Directory /var/www/yourapp>
WSGIProcessGroup yourapp
WSGIApplicationGroup %{GLOBAL}
Order deny,allow
Allow from all
</Directory>
</VirtualHost>
I didn’t test this myself but several Bottle users reported that this works just fine:
import bottle
from google.appengine.ext.webapp import util
# ... add or import your bottle app code here ...
# Do NOT use bottle.run() with AppEngine
util.run_wsgi_app(bottle.default_app())
CGI is slow as hell, but it works:
import bottle
# ... add or import your bottle app code here ...
bottle.run(server=bottle.CGIServer)