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# -*- coding: utf-8 -*-
A microframework based on Werkzeug. It's extensively documented
and follows best practice patterns.
:copyright: (c) 2010 by Armin Ronacher.
:license: BSD, see LICENSE for more details.
from __future__ import with_statement
import os
import sys
from threading import local
from contextlib import contextmanager
from jinja2 import Environment, PackageLoader, FileSystemLoader
from werkzeug import Request as RequestBase, Response as ResponseBase, \
LocalStack, LocalProxy, create_environ, cached_property, \
from werkzeug.routing import Map, Rule
from werkzeug.exceptions import HTTPException, InternalServerError
from werkzeug.contrib.securecookie import SecureCookie
# utilities we import from Werkzeug and Jinja2 that are unused
# in the module but are exported as public interface.
from werkzeug import abort, redirect
from jinja2 import Markup, escape
# use pkg_resource if that works, otherwise fall back to cwd. The
# current working directory is generally not reliable with the notable
# exception of google appengine.
import pkg_resources
except (ImportError, AttributeError, IOError):
pkg_resources = None
class Request(RequestBase):
"""The request object used by default in flask. Remembers the
matched endpoint and view arguments.
It is what ends up as :class:`~flask.request`. If you want to replace
the request object used you can subclass this and set
:attr:`~flask.Flask.request_class` to your subclass.
def __init__(self, environ):
RequestBase.__init__(self, environ)
self.endpoint = None
self.view_args = None
class Response(ResponseBase):
"""The response object that is used by default in flask. Works like the
response object from Werkzeug but is set to have a HTML mimetype by
default. Quite often you don't have to create this object yourself because
:meth:`~flask.Flask.make_response` will take care of that for you.
If you want to replace the response object used you can subclass this and
set :attr:`~flask.Flask.request_class` to your subclass.
default_mimetype = 'text/html'
class _RequestGlobals(object):
class _RequestContext(object):
"""The request context contains all request relevant information. It is
created at the beginning of the request and pushed to the
`_request_ctx_stack` and removed at the end of it. It will create the
URL adapter and request object for the WSGI environment provided.
def __init__(self, app, environ): = app
self.url_adapter = app.url_map.bind_to_environ(environ)
self.request = app.request_class(environ)
self.session = app.open_session(self.request)
self.g = _RequestGlobals()
self.flashes = None
def url_for(endpoint, **values):
"""Generates a URL to the given endpoint with the method provided.
:param endpoint: the endpoint of the URL (name of the function)
:param values: the variable arguments of the URL rule
return, values)
def flash(message):
"""Flashes a message to the next request. In order to remove the
flashed message from the session and to display it to the user,
the template has to call :func:`get_flashed_messages`.
:param message: the message to be flashed.
session['_flashes'] = (session.get('_flashes', [])) + [message]
def get_flashed_messages():
"""Pulls all flashed messages from the session and returns them.
Further calls in the same request to the function will return
the same messages.
flashes =
if flashes is None: = flashes = \
session.pop('_flashes', [])
return flashes
def render_template(template_name, **context):
"""Renders a template from the template folder with the given
:param template_name: the name of the template to be rendered
:param context: the variables that should be available in the
context of the template.
return current_app.jinja_env.get_template(template_name).render(context)
def render_template_string(source, **context):
"""Renders a template from the given template source string
with the given context.
:param template_name: the sourcecode of the template to be
:param context: the variables that should be available in the
context of the template.
return current_app.jinja_env.from_string(source).render(context)
def _default_template_ctx_processor():
"""Default template context processor. Injects `request`,
`session` and `g`.
reqctx =
return dict(
class Flask(object):
"""The flask object implements a WSGI application and acts as the central
object. It is passed the name of the module or package of the
application. Once it is created it will act as a central registry for
the view functions, the URL rules, template configuration and much more.
The name of the package is used to resolve resources from inside the
package or the folder the module is contained in depending on if the
package parameter resolves to an actual python package (a folder with
an `` file inside) or a standard module (just a `.py` file).
For more information about resource loading, see :func:`open_resource`.
Usually you create a :class:`Flask` instance in your main module or
in the `` file of your package like this::
from flask import Flask
app = Flask(__name__)
#: the class that is used for request objects. See :class:`~flask.request`
#: for more information.
request_class = Request
#: the class that is used for response objects. See
#: :class:`~flask.Response` for more information.
response_class = Response
#: path for the static files. If you don't want to use static files
#: you can set this value to `None` in which case no URL rule is added
#: and the development server will no longer serve any static files.
static_path = '/static'
#: if a secret key is set, cryptographic components can use this to
#: sign cookies and other things. Set this to a complex random value
#: when you want to use the secure cookie for instance.
secret_key = None
#: The secure cookie uses this for the name of the session cookie
session_cookie_name = 'session'
#: options that are passed directly to the Jinja2 environment
jinja_options = dict(
extensions=['jinja2.ext.autoescape', 'jinja2.ext.with_']
def __init__(self, package_name):
#: the debug flag. Set this to `True` to enable debugging of
#: the application. In debug mode the debugger will kick in
#: when an unhandled exception ocurrs and the integrated server
#: will automatically reload the application if changes in the
#: code are detected.
self.debug = False
#: the name of the package or module. Do not change this once
#: it was set by the constructor.
self.package_name = package_name
#: where is the app root located?
self.root_path = os.path.abspath(os.path.dirname(
#: a dictionary of all view functions registered. The keys will
#: be function names which are also used to generate URLs and
#: the values are the function objects themselves.
#: to register a view function, use the :meth:`route` decorator.
self.view_functions = {}
#: a dictionary of all registered error handlers. The key is
#: be the error code as integer, the value the function that
#: should handle that error.
#: To register a error handler, use the :meth:`errorhandler`
#: decorator.
self.error_handlers = {}
#: a list of functions that should be called at the beginning
#: of the request before request dispatching kicks in. This
#: can for example be used to open database connections or
#: getting hold of the currently logged in user.
#: To register a function here, use the :meth:`request_init`
#: decorator.
self.request_init_funcs = []
#: a list of functions that are called at the end of the
#: request. Tha function is passed the current response
#: object and modify it in place or replace it.
#: To register a function here use the :meth:`request_shtdown`
#: decorator.
self.request_shutdown_funcs = []
#: a list of functions that are called without arguments
#: to populate the template context. Each returns a dictionary
#: that the template context is updated with.
#: To register a function here, use the :meth:`context_processor`
#: decorator.
self.template_context_processors = [_default_template_ctx_processor]
self.url_map = Map()
if self.static_path is not None:
self.url_map.add(Rule(self.static_path + '/<filename>',
build_only=True, endpoint='static'))
if pkg_resources is not None:
target = (self.package_name, 'static')
target = os.path.join(self.root_path, 'static')
self.wsgi_app = SharedDataMiddleware(self.wsgi_app, {
self.static_path: target
#: the Jinja2 environment. It is created from the
#: :attr:`jinja_options` and the loader that is returned
#: by the :meth:`create_jinja_loader` function.
self.jinja_env = Environment(loader=self.create_jinja_loader(),
def create_jinja_loader(self):
"""Creates the Jinja loader. By default just a package loader for
the configured package is returned that looks up templates in the
`templates` folder. To add other loaders it's possible to
override this method.
if pkg_resources is None:
return FileSystemLoader(os.path.join(self.root_path, 'templates'))
return PackageLoader(self.package_name)
def update_template_context(self, context):
"""Update the template context with some commonly used variables.
This injects request, session and g into the template context.
:param context: the context as a dictionary that is updated in place
to add extra variables.
reqctx =
for func in self.template_context_processors:
def run(self, host='localhost', port=5000, **options):
"""Runs the application on a local development server. If the
:attr:`debug` flag is set the server will automatically reload
for code changes and show a debugger in case an exception happened.
:param host: the hostname to listen on. set this to ``''``
to have the server available externally as well.
:param port: the port of the webserver
:param options: the options to be forwarded to the underlying
Werkzeug server. See :func:`werkzeug.run_simple`
for more information.
from werkzeug import run_simple
if 'debug' in options:
self.debug = options.pop('debug')
options.setdefault('use_reloader', self.debug)
options.setdefault('use_debugger', self.debug)
return run_simple(host, port, self, **options)
def test_client(self):
"""Creates a test client for this application. For information
about unit testing head over to :ref:`testing`.
from werkzeug import Client
return Client(self, self.response_class, use_cookies=True)
def open_resource(self, resource):
"""Opens a resource from the application's resource folder. To see
how this works, consider the following folder structure::
If you want to open the `schema.sql` file you would do the
with app.open_resource('schema.sql') as f:
contents =
:param resource: the name of the resource. To access resources within
subfolders use forward slashes as separator.
if pkg_resources is None:
return open(os.path.join(self.root_path, resource), 'rb')
return pkg_resources.resource_stream(self.package_name, resource)
def open_session(self, request):
"""Creates or opens a new session. Default implementation stores all
session data in a signed cookie. This requires that the
:attr:`secret_key` is set.
:param request: an instance of :attr:`request_class`.
key = self.secret_key
if key is not None:
return SecureCookie.load_cookie(request, self.session_cookie_name,
def save_session(self, session, response):
"""Saves the session if it needs updates. For the default
implementation, check :meth:`open_session`.
:param session: the session to be saved (a
:param response: an instance of :attr:`response_class`
if session is not None:
session.save_cookie(response, self.session_cookie_name)
def add_url_rule(self, rule, endpoint, **options):
"""Connects a URL rule. Works exactly like the :meth:`route`
decorator but does not register the view function for the endpoint.
Basically this example::
def index():
Is equivalent to the following::
def index():
app.add_url_rule('index', '/')
app.view_functions['index'] = index
:param rule: the URL rule as string
:param endpoint: the endpoint for the registered URL rule. Flask
itself assumes the name of the view function as
:param options: the options to be forwarded to the underlying
:class:`~werkzeug.routing.Rule` object
options['endpoint'] = endpoint
options.setdefault('methods', ('GET',))
self.url_map.add(Rule(rule, **options))
def route(self, rule, **options):
"""A decorator that is used to register a view function for a
given URL rule. Example::
def index():
return 'Hello World'
Variables 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
The following converters are possible:
=========== ===========================================
`int` accepts integers
`float` like `int` but for floating point values
`path` like the default but also accepts slashes
=========== ===========================================
Here some examples::
def index():
def show_user(username):
def show_post(post_id):
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
1. 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.
2. If a rule does not end with a trailing slash and the user request
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.
The :meth:`route` decorator accepts a couple of other arguments
as well:
:param rule: the URL rule as string
:param methods: a list of methods this rule should be limited
to (``GET``, ``POST`` etc.). By default a rule
just listens for ``GET`` (and implicitly ``HEAD``).
:param subdomain: specifies the rule for the subdoain in case
subdomain matching is in use.
:param strict_slashes: can be used to disable the strict slashes
setting for this rule. See above.
:param options: other options to be forwarded to the underlying
:class:`~werkzeug.routing.Rule` object.
def decorator(f):
self.add_url_rule(rule, f.__name__, **options)
self.view_functions[f.__name__] = f
return f
return decorator
def errorhandler(self, code):
"""A decorator that is used to register a function give a given
error code. Example::
def page_not_found():
return 'This page does not exist', 404
You can also register a function as error handler without using
the :meth:`errorhandler` decorator. The following example is
equivalent to the one above::
def page_not_found():
return 'This page does not exist', 404
app.error_handlers[404] = page_not_found
:param code: the code as integer for the handler
def decorator(f):
self.error_handlers[code] = f
return f
return decorator
def request_init(self, f):
"""Registers a function to run before each request."""
return f
def request_shutdown(self, f):
"""Register a function to be run after each request."""
return f
def context_processor(self, f):
"""Registers a template context processor function."""
return f
def match_request(self):
"""Matches the current request against the URL map and also
stores the endpoint and view arguments on the request object
is successful, otherwise the exception is stored.
rv =
request.endpoint, request.view_args = rv
return rv
def dispatch_request(self):
"""Does the request dispatching. Matches the URL and returns the
return value of the view or error handler. This does not have to
be a response object. In order to convert the return value to a
proper response object, call :func:`make_response`.
endpoint, values = self.match_request()
return self.view_functions[endpoint](**values)
except HTTPException, e:
handler = self.error_handlers.get(e.code)
if handler is None:
return e
return handler(e)
except Exception, e:
handler = self.error_handlers.get(500)
if self.debug or handler is None:
return handler(e)
def make_response(self, rv):
"""Converts the return value from a view function to a real
response object that is an instance of :attr:`response_class`.
The following types are allowd for `rv`:
======================= ===========================================
:attr:`response_class` the object is returned unchanged
:class:`str` a response object is created with the
string as body
:class:`unicode` a response object is created with the
string encoded to utf-8 as body
:class:`tuple` the response object is created with the
contents of the tuple as arguments
a WSGI function the function is called as WSGI application
and buffered as response object
======================= ===========================================
:param rv: the return value from the view function
if isinstance(rv, self.response_class):
return rv
if isinstance(rv, basestring):
return self.response_class(rv)
if isinstance(rv, tuple):
return self.response_class(*rv)
return self.response_class.force_type(rv, request.environ)
def preprocess_request(self):
"""Called before the actual request dispatching and will
call every as :func:`request_init` decorated function.
If any of these function returns a value it's handled as
if it was the return value from the view and further
request handling is stopped.
for func in self.request_init_funcs:
rv = func()
if rv is not None:
return rv
def process_response(self, response):
"""Can be overridden in order to modify the response object
before it's sent to the WSGI server.
:param response: a :attr:`response_class` object.
:return: a new response object or the same, has to be an
instance of :attr:`response_class`.
session =
if session is not None:
self.save_session(session, response)
for handler in self.request_shutdown_funcs:
response = handler(response)
return response
def wsgi_app(self, environ, start_response):
"""The actual WSGI application. This is not implemented in
`__call__` so that middlewares can be applied:
app.wsgi_app = MyMiddleware(app.wsgi_app)
:param environ: a WSGI environment
:param start_response: a callable accepting a status code,
a list of headers and an optional
exception context to start the response
with self.request_context(environ):
rv = self.preprocess_request()
if rv is None:
rv = self.dispatch_request()
response = self.make_response(rv)
response = self.process_response(response)
return response(environ, start_response)
def request_context(self, environ):
"""Creates a request context from the given environment and binds
it to the current context. This must be used in combination with
the `with` statement because the request is only bound to the
current context for the duration of the `with` block.
Example usage::
with app.request_context(environ):
:params environ: a WSGI environment
_request_ctx_stack.push(_RequestContext(self, environ))
def test_request_context(self, *args, **kwargs):
"""Creates a WSGI environment from the given values (see
:func:`werkzeug.create_environ` for more information, this
function accepts the same arguments).
return self.request_context(create_environ(*args, **kwargs))
def __call__(self, environ, start_response):
"""Shortcut for :attr:`wsgi_app`"""
return self.wsgi_app(environ, start_response)
# context locals
_request_ctx_stack = LocalStack()
current_app = LocalProxy(lambda:
request = LocalProxy(lambda:
session = LocalProxy(lambda:
g = LocalProxy(lambda: