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# -*- coding: utf-8 -*-
This module implements the central WSGI application object.
:copyright: (c) 2011 by Armin Ronacher.
:license: BSD, see LICENSE for more details.
from __future__ import with_statement
import os
import sys
from threading import Lock
from datetime import timedelta
from itertools import chain
from functools import update_wrapper
from werkzeug.datastructures import ImmutableDict
from werkzeug.routing import Map, Rule, RequestRedirect
from werkzeug.exceptions import HTTPException, InternalServerError, \
MethodNotAllowed, BadRequest
from .helpers import _PackageBoundObject, url_for, get_flashed_messages, \
locked_cached_property, _tojson_filter, _endpoint_from_view_func, \
from .wrappers import Request, Response
from .config import ConfigAttribute, Config
from .ctx import RequestContext
from .globals import _request_ctx_stack, request
from .sessions import SecureCookieSessionInterface
from .module import blueprint_is_module
from .templating import DispatchingJinjaLoader, Environment, \
from .signals import request_started, request_finished, got_request_exception, \
# a lock used for logger initialization
_logger_lock = Lock()
def setupmethod(f):
"""Wraps a method so that it performs a check in debug mode if the
first request was already handled.
def wrapper_func(self, *args, **kwargs):
if self.debug and self._got_first_request:
raise AssertionError('A setup function was called after the '
'first request was handled. This usually indicates a bug '
'in the application where a module was not imported '
'and decorators or other functionality was called too late.\n'
'To fix this make sure to import all your view modules, '
'database models and everything related at a central place '
'before the application starts serving requests.')
return f(self, *args, **kwargs)
return update_wrapper(wrapper_func, f)
class Flask(_PackageBoundObject):
"""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__)
.. admonition:: About the First Parameter
The idea of the first parameter is to give Flask an idea what
belongs to your application. This name is used to find resources
on the file system, can be used by extensions to improve debugging
information and a lot more.
So it's important what you provide there. If you are using a single
module, `__name__` is always the correct value. If you however are
using a package, it's usually recommended to hardcode the name of
your package there.
For example if your application is defined in `yourapplication/`
you should create it with one of the two versions below::
app = Flask('yourapplication')
app = Flask(__name__.split('.')[0])
Why is that? The application will work even with `__name__`, thanks
to how resources are looked up. However it will make debugging more
painful. Certain extensions can make assumptions based on the
import name of your application. For example the Flask-SQLAlchemy
extension will look for the code in your application that triggered
an SQL query in debug mode. If the import name is not properly set
up, that debugging information is lost. (For example it would only
pick up SQL queries in `` and not
.. versionadded:: 0.7
The `static_url_path`, `static_folder`, and `template_folder`
parameters were added.
.. versionadded:: 0.8
The `instance_path` and `instance_relative_config` parameters were
:param import_name: the name of the application package
:param static_url_path: can be used to specify a different path for the
static files on the web. Defaults to the name
of the `static_folder` folder.
:param static_folder: the folder with static files that should be served
at `static_url_path`. Defaults to the ``'static'``
folder in the root path of the application.
:param template_folder: the folder that contains the templates that should
be used by the application. Defaults to
``'templates'`` folder in the root path of the
:param instance_path: An alternative instance path for the application.
By default the folder ``'instance'`` next to the
package or module is assumed to be the instance
:param instance_relative_config: if set to `True` relative filenames
for loading the config are assumed to
be relative to the instance path instead
of the application root.
#: 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
#: 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.
#: This attribute can also be configured from the config with the `DEBUG`
#: configuration key. Defaults to `False`.
debug = ConfigAttribute('DEBUG')
#: The testing flag. Set this to `True` to enable the test mode of
#: Flask extensions (and in the future probably also Flask itself).
#: For example this might activate unittest helpers that have an
#: additional runtime cost which should not be enabled by default.
#: If this is enabled and PROPAGATE_EXCEPTIONS is not changed from the
#: default it's implicitly enabled.
#: This attribute can also be configured from the config with the
#: `TESTING` configuration key. Defaults to `False`.
testing = ConfigAttribute('TESTING')
#: 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.
#: This attribute can also be configured from the config with the
#: `SECRET_KEY` configuration key. Defaults to `None`.
secret_key = ConfigAttribute('SECRET_KEY')
#: The secure cookie uses this for the name of the session cookie.
#: This attribute can also be configured from the config with the
#: `SESSION_COOKIE_NAME` configuration key. Defaults to ``'session'``
session_cookie_name = ConfigAttribute('SESSION_COOKIE_NAME')
#: A :class:`~datetime.timedelta` which is used to set the expiration
#: date of a permanent session. The default is 31 days which makes a
#: permanent session survive for roughly one month.
#: This attribute can also be configured from the config with the
#: `PERMANENT_SESSION_LIFETIME` configuration key. Defaults to
#: ``timedelta(days=31)``
permanent_session_lifetime = ConfigAttribute('PERMANENT_SESSION_LIFETIME')
#: Enable this if you want to use the X-Sendfile feature. Keep in
#: mind that the server has to support this. This only affects files
#: sent with the :func:`send_file` method.
#: .. versionadded:: 0.2
#: This attribute can also be configured from the config with the
#: `USE_X_SENDFILE` configuration key. Defaults to `False`.
use_x_sendfile = ConfigAttribute('USE_X_SENDFILE')
#: The name of the logger to use. By default the logger name is the
#: package name passed to the constructor.
#: .. versionadded:: 0.4
logger_name = ConfigAttribute('LOGGER_NAME')
#: Enable the deprecated module support? This is active by default
#: in 0.7 but will be changed to False in 0.8. With Flask 1.0 modules
#: will be removed in favor of Blueprints
enable_modules = True
#: The logging format used for the debug logger. This is only used when
#: the application is in debug mode, otherwise the attached logging
#: handler does the formatting.
#: .. versionadded:: 0.3
debug_log_format = (
'-' * 80 + '\n' +
'%(levelname)s in %(module)s [%(pathname)s:%(lineno)d]:\n' +
'%(message)s\n' +
'-' * 80
#: Options that are passed directly to the Jinja2 environment.
jinja_options = ImmutableDict(
extensions=['jinja2.ext.autoescape', 'jinja2.ext.with_']
#: Default configuration parameters.
default_config = ImmutableDict({
'DEBUG': False,
'TESTING': False,
'PERMANENT_SESSION_LIFETIME': timedelta(days=31),
#: The rule object to use for URL rules created. This is used by
#: :meth:`add_url_rule`. Defaults to :class:`werkzeug.routing.Rule`.
#: .. versionadded:: 0.7
url_rule_class = Rule
#: the test client that is used with when `test_client` is used.
#: .. versionadded:: 0.7
test_client_class = None
#: the session interface to use. By default an instance of
#: :class:`~flask.sessions.SecureCookieSessionInterface` is used here.
#: .. versionadded:: 0.8
session_interface = SecureCookieSessionInterface()
def __init__(self, import_name, static_path=None, static_url_path=None,
static_folder='static', template_folder='templates',
instance_path=None, instance_relative_config=False):
_PackageBoundObject.__init__(self, import_name,
if static_path is not None:
from warnings import warn
warn(DeprecationWarning('static_path is now called '
'static_url_path'), stacklevel=2)
static_url_path = static_path
if static_url_path is not None:
self.static_url_path = static_url_path
if static_folder is not None:
self.static_folder = static_folder
if instance_path is None:
instance_path = self.auto_find_instance_path()
elif not os.path.isabs(instance_path):
raise ValueError('If an instance path is provided it must be '
'absolute. A relative path was given instead.')
#: Holds the path to the instance folder.
#: .. versionadded:: 0.8
self.instance_path = instance_path
#: The configuration dictionary as :class:`Config`. This behaves
#: exactly like a regular dictionary but supports additional methods
#: to load a config from files.
self.config = self.make_config(instance_relative_config)
# Prepare the deferred setup of the logger.
self._logger = None
self.logger_name = self.import_name
#: 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 = {}
# support for the now deprecated `error_handlers` attribute. The
# :attr:`error_handler_spec` shall be used now.
self._error_handlers = {}
#: A dictionary of all registered error handlers. The key is `None`
#: for error handlers active on the application, otherwise the key is
#: the name of the blueprint. Each key points to another dictionary
#: where they key is the status code of the http exception. The
#: special key `None` points to a list of tuples where the first item
#: is the class for the instance check and the second the error handler
#: function.
#: To register a error handler, use the :meth:`errorhandler`
#: decorator.
self.error_handler_spec = {None: self._error_handlers}
#: A dictionary with lists of functions that should be called at the
#: beginning of the request. The key of the dictionary is the name of
#: the blueprint this function is active for, `None` for all requests.
#: 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:`before_request` decorator.
self.before_request_funcs = {}
#: A lists of functions that should be called at the beginning of the
#: first request to this instance. To register a function here, use
#: the :meth:`before_first_request` decorator.
#: .. versionadded:: 0.8
self.before_first_request_funcs = []
#: A dictionary with lists of functions that should be called after
#: each request. The key of the dictionary is the name of the blueprint
#: this function is active for, `None` for all requests. 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:`after_request` decorator.
self.after_request_funcs = {}
#: A dictionary with lists of functions that are called after
#: each request, even if an exception has occurred. The key of the
#: dictionary is the name of the blueprint this function is active for,
#: `None` for all requests. These functions are not allowed to modify
#: the request, and their return values are ignored. If an exception
#: occurred while processing the request, it gets passed to each
#: teardown_request function. To register a function here, use the
#: :meth:`teardown_request` decorator.
#: .. versionadded:: 0.7
self.teardown_request_funcs = {}
#: A dictionary with lists of functions that can be used as URL
#: value processor functions. Whenever a URL is built these functions
#: are called to modify the dictionary of values in place. The key
#: `None` here is used for application wide
#: callbacks, otherwise the key is the name of the blueprint.
#: Each of these functions has the chance to modify the dictionary
#: .. versionadded:: 0.7
self.url_value_preprocessors = {}
#: A dictionary with lists of functions that can be used as URL value
#: preprocessors. The key `None` here is used for application wide
#: callbacks, otherwise the key is the name of the blueprint.
#: Each of these functions has the chance to modify the dictionary
#: of URL values before they are used as the keyword arguments of the
#: view function. For each function registered this one should also
#: provide a :meth:`url_defaults` function that adds the parameters
#: automatically again that were removed that way.
#: .. versionadded:: 0.7
self.url_default_functions = {}
#: A dictionary with list of functions that are called without argument
#: to populate the template context. The key of the dictionary is the
#: name of the blueprint this function is active for, `None` for all
#: requests. 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 = {
None: [_default_template_ctx_processor]
#: all the attached blueprints in a directory by name. Blueprints
#: can be attached multiple times so this dictionary does not tell
#: you how often they got attached.
#: .. versionadded:: 0.7
self.blueprints = {}
#: a place where extensions can store application specific state. For
#: example this is where an extension could store database engines and
#: similar things. For backwards compatibility extensions should register
#: themselves like this::
#: if not hasattr(app, 'extensions'):
#: app.extensions = {}
#: app.extensions['extensionname'] = SomeObject()
#: The key must match the name of the `flaskext` module. For example in
#: case of a "Flask-Foo" extension in ``, the key would be
#: ``'foo'``.
#: .. versionadded:: 0.7
self.extensions = {}
#: The :class:`~werkzeug.routing.Map` for this instance. You can use
#: this to change the routing converters after the class was created
#: but before any routes are connected. Example::
#: from werkzeug.routing import BaseConverter
#: class ListConverter(BaseConverter):
#: def to_python(self, value):
#: return value.split(',')
#: def to_url(self, values):
#: return ','.join(BaseConverter.to_url(value)
#: for value in values)
#: app = Flask(__name__)
#: app.url_map.converters['list'] = ListConverter
self.url_map = Map()
# tracks internally if the application already handled at least one
# request.
self._got_first_request = False
self._before_request_lock = Lock()
# register the static folder for the application. Do that even
# if the folder does not exist. First of all it might be created
# while the server is running (usually happens during development)
# but also because google appengine stores static files somewhere
# else when mapped with the .yml file.
if self.has_static_folder:
self.add_url_rule(self.static_url_path + '/<path:filename>',
def _get_error_handlers(self):
from warnings import warn
warn(DeprecationWarning('error_handlers is deprecated, use the '
'new error_handler_spec attribute instead.'), stacklevel=1)
return self._error_handlers
def _set_error_handlers(self, value):
self._error_handlers = value
self.error_handler_spec[None] = value
error_handlers = property(_get_error_handlers, _set_error_handlers)
del _get_error_handlers, _set_error_handlers
def name(self):
"""The name of the application. This is usually the import name
with the difference that it's guessed from the run file if the
import name is main. This name is used as a display name when
Flask needs the name of the application. It can be set and overriden
to change the value.
.. versionadded:: 0.8
if self.import_name == '__main__':
fn = getattr(sys.modules['__main__'], '__file__', None)
if fn is None:
return 'unknown'
return os.path.splitext(os.path.basename(fn))[0]
return self.import_name
def propagate_exceptions(self):
"""Returns the value of the `PROPAGATE_EXCEPTIONS` configuration
value in case it's set, otherwise a sensible default is returned.
.. versionadded:: 0.7
rv = self.config['PROPAGATE_EXCEPTIONS']
if rv is not None:
return rv
return self.testing or self.debug
def preserve_context_on_exception(self):
"""Returns the value of the `PRESERVE_CONTEXT_ON_EXCEPTION`
configuration value in case it's set, otherwise a sensible default
is returned.
.. versionadded:: 0.7
if rv is not None:
return rv
return self.debug
def logger(self):
"""A :class:`logging.Logger` object for this application. The
default configuration is to log to stderr if the application is
in debug mode. This logger can be used to (surprise) log messages.
Here some examples::
app.logger.debug('A value for debugging')
app.logger.warning('A warning ocurred (%d apples)', 42)
app.logger.error('An error occoured')
.. versionadded:: 0.3
if self._logger and == self.logger_name:
return self._logger
with _logger_lock:
if self._logger and == self.logger_name:
return self._logger
from flask.logging import create_logger
self._logger = rv = create_logger(self)
return rv
def jinja_env(self):
"""The Jinja2 environment used to load templates."""
rv = self.create_jinja_environment()
# Hack to support the init_jinja_globals method which is supported
# until 1.0 but has an API deficiency.
if getattr(self.init_jinja_globals, 'im_func', None) is not \
from warnings import warn
warn(DeprecationWarning('This flask class uses a customized '
'init_jinja_globals() method which is deprecated. '
'Move the code from that method into the '
'create_jinja_environment() method instead.'))
self.__dict__['jinja_env'] = rv
return rv
def got_first_request(self):
"""This attribute is set to `True` if the application started
handling the first request.
.. versionadded:: 0.8
return self._got_first_request
def make_config(self, instance_relative=False):
"""Used to create the config attribute by the Flask constructor.
The `instance_relative` parameter is passed in from the constructor
of Flask (there named `instance_relative_config`) and indicates if
the config should be relative to the instance path or the root path
of the application.
.. versionadded:: 0.8
root_path = self.root_path
if instance_relative:
root_path = self.instance_path
return Config(root_path, self.default_config)
def auto_find_instance_path(self):
"""Tries to locate the instance path if it was not provided to the
constructor of the application class. It will basically calculate
the path to a folder named ``instance`` next to your main file or
the package.
.. versionadded:: 0.8
prefix, package_path = find_package(self.import_name)
if prefix is None:
return os.path.join(package_path, 'instance')
return os.path.join(prefix, 'var', + '-instance')
def open_instance_resource(self, resource, mode='rb'):
"""Opens a resource from the application's instance folder
(:attr:`instance_path`). Otherwise works like
:meth:`open_resource`. Instance resources can also be opened for
:param resource: the name of the resource. To access resources within
subfolders use forward slashes as separator.
return open(os.path.join(self.instance_path, resource), mode)
def create_jinja_environment(self):
"""Creates the Jinja2 environment based on :attr:`jinja_options`
and :meth:`select_jinja_autoescape`. Since 0.7 this also adds
the Jinja2 globals and filters after initialization. Override
this function to customize the behavior.
.. versionadded:: 0.5
options = dict(self.jinja_options)
if 'autoescape' not in options:
options['autoescape'] = self.select_jinja_autoescape
rv = Environment(self, **options)
rv.filters['tojson'] = _tojson_filter
return rv
def create_global_jinja_loader(self):
"""Creates the loader for the Jinja2 environment. Can be used to
override just the loader and keeping the rest unchanged. It's
discouraged to override this function. Instead one should override
the :meth:`jinja_loader` function instead.
The global loader dispatches between the loaders of the application
and the individual blueprints.
.. versionadded:: 0.7
return DispatchingJinjaLoader(self)
def init_jinja_globals(self):
"""Deprecated. Used to initialize the Jinja2 globals.
.. versionadded:: 0.5
.. versionchanged:: 0.7
This method is deprecated with 0.7. Override
:meth:`create_jinja_environment` instead.
def select_jinja_autoescape(self, filename):
"""Returns `True` if autoescaping should be active for the given
template name.
.. versionadded:: 0.5
if filename is None:
return False
return filename.endswith(('.html', '.htm', '.xml', '.xhtml'))
def update_template_context(self, context):
"""Update the template context with some commonly used variables.
This injects request, session, config and g into the template
context as well as everything template context processors want
to inject. Note that the as of Flask 0.6, the original values
in the context will not be overriden if a context processor
decides to return a value with the same key.
:param context: the context as a dictionary that is updated in place
to add extra variables.
funcs = self.template_context_processors[None]
bp =
if bp is not None and bp in self.template_context_processors:
funcs = chain(funcs, self.template_context_processors[bp])
orig_ctx = context.copy()
for func in funcs:
# make sure the original values win. This makes it possible to
# easier add new variables in context processors without breaking
# existing views.
def run(self, host='', port=5000, debug=None, **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.
If you want to run the application in debug mode, but disable the
code execution on the interactive debugger, you can pass
``use_evalex=False`` as parameter. This will keep the debugger's
traceback screen active, but disable code execution.
.. admonition:: Keep in Mind
Flask will suppress any server error with a generic error page
unless it is in debug mode. As such to enable just the
interactive debugger without the code reloading, you have to
invoke :meth:`run` with ``debug=True`` and ``use_reloader=False``.
Setting ``use_debugger`` to `True` without being in debug mode
won't catch any exceptions because there won't be any to
: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 debug: if given, enable or disable debug mode.
See :attr:`debug`.
:param options: the options to be forwarded to the underlying
Werkzeug server. See
:func:`werkzeug.serving.run_simple` for more
from werkzeug.serving import run_simple
if debug is not None:
self.debug = bool(debug)
options.setdefault('use_reloader', self.debug)
options.setdefault('use_debugger', self.debug)
run_simple(host, port, self, **options)
# reset the first request information if the development server
# resetted normally. This makes it possible to restart the server
# without reloader and that stuff from an interactive shell.
self._got_first_request = False
def test_client(self, use_cookies=True):
"""Creates a test client for this application. For information
about unit testing head over to :ref:`testing`.
The test client can be used in a `with` block to defer the closing down
of the context until the end of the `with` block. This is useful if
you want to access the context locals for testing::
with app.test_client() as c:
rv = c.get('/?vodka=42')
assert request.args['vodka'] == '42'
See :class:`~flask.testing.FlaskClient` for more information.
.. versionchanged:: 0.4
added support for `with` block usage for the client.
.. versionadded:: 0.7
The `use_cookies` parameter was added as well as the ability
to override the client to be used by setting the
:attr:`test_client_class` attribute.
cls = self.test_client_class
if cls is None:
from flask.testing import FlaskClient as cls
return cls(self, self.response_class, use_cookies=use_cookies)
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. Instead of overriding this method
we recommend replacing the :class:`session_interface`.
:param request: an instance of :attr:`request_class`.
return self.session_interface.open_session(self, request)
def save_session(self, session, response):
"""Saves the session if it needs updates. For the default
implementation, check :meth:`open_session`. Instead of overriding this
method we recommend replacing the :class:`session_interface`.
:param session: the session to be saved (a
:param response: an instance of :attr:`response_class`
return self.session_interface.save_session(self, session, response)
def make_null_session(self):
"""Creates a new instance of a missing session. Instead of overriding
this method we recommend replacing the :class:`session_interface`.
.. versionadded:: 0.7
return self.session_interface.make_null_session(self)
def register_module(self, module, **options):
"""Registers a module with this application. The keyword argument
of this function are the same as the ones for the constructor of the
:class:`Module` class and will override the values of the module if
.. versionchanged:: 0.7
The module system was deprecated in favor for the blueprint
assert blueprint_is_module(module), 'register_module requires ' \
'actual module objects. Please upgrade to blueprints though.'
if not self.enable_modules:
raise RuntimeError('Module support was disabled but code '
'attempted to register a module named %r' % module)
from warnings import warn
warn(DeprecationWarning('Modules are deprecated. Upgrade to '
'using blueprints. Have a look into the documentation for '
'more information. If this module was registered by a '
'Flask-Extension upgrade the extension or contact the author '
'of that extension instead. (Registered %r)' % module),
self.register_blueprint(module, **options)
def register_blueprint(self, blueprint, **options):
"""Registers a blueprint on the application.
.. versionadded:: 0.7
first_registration = False
if in self.blueprints:
assert self.blueprints[] is blueprint, \
'A blueprint\'s name collision ocurred between %r and ' \
'%r. Both share the same name "%s". Blueprints that ' \
'are created on the fly need unique names.' % \
(blueprint, self.blueprints[],
self.blueprints[] = blueprint
first_registration = True
blueprint.register(self, options, first_registration)
def add_url_rule(self, rule, endpoint=None, view_func=None, **options):
"""Connects a URL rule. Works exactly like the :meth:`route`
decorator. If a view_func is provided it will be registered with the
Basically this example::
def index():
Is equivalent to the following::
def index():
app.add_url_rule('/', 'index', index)
If the view_func is not provided you will need to connect the endpoint
to a view function like so::
app.view_functions['index'] = index
If a view function is provided some defaults can be specified directly
on the view function. For more information refer to
.. versionchanged:: 0.2
`view_func` parameter added.
.. versionchanged:: 0.6
`OPTIONS` is added automatically as method.
: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 view_func: the function to call when serving a request to the
provided endpoint
:param options: the options to be forwarded to the underlying
:class:`~werkzeug.routing.Rule` object. A change
to Werkzeug is handling of method options. methods
is a list of methods this rule should be limited
to (`GET`, `POST` etc.). By default a rule
just listens for `GET` (and implicitly `HEAD`).
Starting with Flask 0.6, `OPTIONS` is implicitly
added and handled by the standard request handling.
if endpoint is None:
endpoint = _endpoint_from_view_func(view_func)
options['endpoint'] = endpoint
methods = options.pop('methods', None)
# if the methods are not given and the view_func object knows its
# methods we can use that instead. If neither exists, we go with
# a tuple of only `GET` as default.
if methods is None:
methods = getattr(view_func, 'methods', None) or ('GET',)
# starting with Flask 0.8 the view_func object can disable and
# force-enable the automatic options handling.
provide_automatic_options = getattr(view_func,
'provide_automatic_options', None)
if provide_automatic_options is None:
if 'OPTIONS' not in methods:
methods = tuple(methods) + ('OPTIONS',)
provide_automatic_options = True
provide_automatic_options = False
# due to a werkzeug bug we need to make sure that the defaults are
# None if they are an empty dictionary. This should not be necessary
# with Werkzeug 0.7
options['defaults'] = options.get('defaults') or None
rule = self.url_rule_class(rule, methods=methods, **options)
rule.provide_automatic_options = provide_automatic_options
if view_func is not None:
self.view_functions[endpoint] = view_func
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`).
Starting with Flask 0.6, `OPTIONS` is implicitly
added and handled by the standard request handling.
:param subdomain: specifies the rule for the subdomain 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 endpoint: Since version 0.8 you can also pass the enpoint,
it will be used instead of generating the endpoint
from the function name.
:param options: other options to be forwarded to the underlying
:class:`~werkzeug.routing.Rule` object.
def decorator(f):
endpoint = options.pop('endpoint', None)
self.add_url_rule(rule, endpoint, f, **options)
return f
return decorator
def endpoint(self, endpoint):
"""A decorator to register a function as an endpoint.
def example():
return "example"
:param endpoint: the name of the endpoint
def decorator(f):
self.view_functions[endpoint] = f
return f
return decorator
def errorhandler(self, code_or_exception):
"""A decorator that is used to register a function give a given
error code. Example::
def page_not_found(error):
return 'This page does not exist', 404
You can also register handlers for arbitrary exceptions::
def special_exception_handler(error):
return 'Database connection failed', 500
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(error):
return 'This page does not exist', 404
app.error_handler_spec[None][404] = page_not_found
Setting error handlers via assignments to :attr:`error_handler_spec`
however is discouraged as it requires fidling with nested dictionaries
and the special case for arbitrary exception types.
The first `None` refers to the active blueprint. If the error
handler should be application wide `None` shall be used.
.. versionadded:: 0.7
One can now additionally also register custom exception types
that do not necessarily have to be a subclass of the
:class:`~werkzeug.exceptions.HTTPException` class.
:param code: the code as integer for the handler
def decorator(f):
self._register_error_handler(None, code_or_exception, f)
return f
return decorator
def register_error_handler(self, code_or_exception, f):
"""Alternative error attach function to the :meth:`errorhandler`
decorator that is more straightforward to use for non decorator
.. versionadded:: 0.7
self._register_error_handler(None, code_or_exception, f)
def _register_error_handler(self, key, code_or_exception, f):
if isinstance(code_or_exception, HTTPException):
code_or_exception = code_or_exception.code
if isinstance(code_or_exception, (int, long)):
assert code_or_exception != 500 or key is None, \
'It is currently not possible to register a 500 internal ' \
'server error on a per-blueprint level.'
self.error_handler_spec.setdefault(key, {})[code_or_exception] = f
self.error_handler_spec.setdefault(key, {}).setdefault(None, []) \
.append((code_or_exception, f))
def template_filter(self, name=None):
"""A decorator that is used to register custom template filter.
You can specify a name for the filter, otherwise the function
name will be used. Example::
def reverse(s):
return s[::-1]
:param name: the optional name of the filter, otherwise the
function name will be used.
def decorator(f):
self.jinja_env.filters[name or f.__name__] = f
return f
return decorator
def before_request(self, f):
"""Registers a function to run before each request."""
self.before_request_funcs.setdefault(None, []).append(f)
return f
def before_first_request(self, f):
"""Registers a function to be run before the first request to this
instance of the application.
.. versionadded:: 0.8
def after_request(self, f):
"""Register a function to be run after each request. Your function
must take one parameter, a :attr:`response_class` object and return
a new response object or the same (see :meth:`process_response`).
As of Flask 0.7 this function might not be executed at the end of the
request in case an unhandled exception ocurred.
self.after_request_funcs.setdefault(None, []).append(f)
return f
def teardown_request(self, f):
"""Register a function to be run at the end of each request,
regardless of whether there was an exception or not. These functions
are executed when the request context is popped, even if not an
actual request was performed.
ctx = app.test_request_context()
When ``ctx.pop()`` is executed in the above example, the teardown
functions are called just before the request context moves from the
stack of active contexts. This becomes relevant if you are using
such constructs in tests.
Generally teardown functions must take every necesary step to avoid
that they will fail. If they do execute code that might fail they
will have to surround the execution of these code by try/except
statements and log ocurring errors.
self.teardown_request_funcs.setdefault(None, []).append(f)
return f
def context_processor(self, f):
"""Registers a template context processor function."""
return f
def url_value_preprocessor(self, f):
"""Registers a function as URL value preprocessor for all view
functions of the application. It's called before the view functions
are called and can modify the url values provided.
self.url_value_preprocessors.setdefault(None, []).append(f)
return f
def url_defaults(self, f):
"""Callback function for URL defaults for all view functions of the
application. It's called with the endpoint and values and should
update the values passed in place.
self.url_default_functions.setdefault(None, []).append(f)
return f
def handle_http_exception(self, e):
"""Handles an HTTP exception. By default this will invoke the
registered error handlers and fall back to returning the
exception as response.
.. versionadded: 0.3
handlers = self.error_handler_spec.get(request.blueprint)
if handlers and e.code in handlers:
handler = handlers[e.code]
handler = self.error_handler_spec[None].get(e.code)
if handler is None:
return e
return handler(e)
def trap_http_exception(self, e):
"""Checks if an HTTP exception should be trapped or not. By default
this will return `False` for all exceptions except for a bad request
key error if ``TRAP_BAD_REQUEST_ERRORS`` is set to `True`. It
also returns `True` if ``TRAP_HTTP_EXCEPTIONS`` is set to `True`.
This is called for all HTTP exceptions raised by a view function.
If it returns `True` for any exception the error handler for this
exception is not called and it shows up as regular exception in the
traceback. This is helpful for debugging implicitly raised HTTP
.. versionadded:: 0.8
if self.config['TRAP_HTTP_EXCEPTIONS']:
return True
if self.config['TRAP_BAD_REQUEST_ERRORS']:
return isinstance(e, BadRequest)
return False
def handle_user_exception(self, e):
"""This method is called whenever an exception occurs that should be
handled. A special case are
:class:`~werkzeug.exception.HTTPException`\s which are forwarded by
this function to the :meth:`handle_http_exception` method. This
function will either return a response value or reraise the
exception with the same traceback.
.. versionadded:: 0.7
exc_type, exc_value, tb = sys.exc_info()
assert exc_value is e
# ensure not to trash sys.exc_info() at that point in case someone
# wants the traceback preserved in handle_http_exception. Of course
# we cannot prevent users from trashing it themselves in a custom
# trap_http_exception method so that's their fault then.
if isinstance(e, HTTPException) and not self.trap_http_exception(e):
return self.handle_http_exception(e)
blueprint_handlers = ()
handlers = self.error_handler_spec.get(request.blueprint)
if handlers is not None:
blueprint_handlers = handlers.get(None, ())
app_handlers = self.error_handler_spec[None].get(None, ())
for typecheck, handler in chain(blueprint_handlers, app_handlers):
if isinstance(e, typecheck):
return handler(e)
raise exc_type, exc_value, tb
def handle_exception(self, e):
"""Default exception handling that kicks in when an exception
occours that is not caught. In debug mode the exception will
be re-raised immediately, otherwise it is logged and the handler
for a 500 internal server error is used. If no such handler
exists, a default 500 internal server error message is displayed.
.. versionadded: 0.3
exc_type, exc_value, tb = sys.exc_info()
got_request_exception.send(self, exception=e)
handler = self.error_handler_spec[None].get(500)
if self.propagate_exceptions:
# if we want to repropagate the exception, we can attempt to
# raise it with the whole traceback in case we can do that
# (the function was actually called from the except part)
# otherwise, we just raise the error again
if exc_value is e:
raise exc_type, exc_value, tb
raise e
self.log_exception((exc_type, exc_value, tb))
if handler is None:
return InternalServerError()
return handler(e)
def log_exception(self, exc_info):
"""Logs an exception. This is called by :meth:`handle_exception`
if debugging is disabled and right before the handler is called.
The default implementation logs the exception as error on the
.. versionadded:: 0.8
self.logger.error('Exception on %s [%s]' % (
), exc_info=exc_info)
def raise_routing_exception(self, request):
"""Exceptions that are recording during routing are reraised with
this method. During debug we are not reraising redirect requests
for non ``GET``, ``HEAD``, or ``OPTIONS`` requests and we're raising
a different error instead to help debug situations.
if not self.debug \
or not isinstance(request.routing_exception, RequestRedirect) \
or request.method in ('GET', 'HEAD', 'OPTIONS'):
raise request.routing_exception
from .debughelpers import FormDataRoutingRedirect
raise FormDataRoutingRedirect(request)
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`.
.. versionchanged:: 0.7
This no longer does the exception handling, this code was
moved to the new :meth:`full_dispatch_request`.
req =
if req.routing_exception is not None:
rule = req.url_rule
# if we provide automatic options for this URL and the
# request came with the OPTIONS method, reply automatically
if getattr(rule, 'provide_automatic_options', False) \
and req.method == 'OPTIONS':
return self.make_default_options_response()
# otherwise dispatch to the handler for that endpoint
return self.view_functions[rule.endpoint](**req.view_args)
def full_dispatch_request(self):
"""Dispatches the request and on top of that performs request
pre and postprocessing as well as HTTP exception catching and
error handling.
.. versionadded:: 0.7
rv = self.preprocess_request()
if rv is None:
rv = self.dispatch_request()
except Exception, e:
rv = self.handle_user_exception(e)
response = self.make_response(rv)
response = self.process_response(response)
request_finished.send(self, response=response)
return response
def try_trigger_before_first_request_functions(self):
"""Called before each request and will ensure that it triggers
the :attr:`before_first_request_funcs` and only exactly once per
application instance (which means process usually).
if self._got_first_request:
with self._before_request_lock:
if self._got_first_request:
self._got_first_request = True
for func in self.before_first_request_funcs:
def make_default_options_response(self):
"""This method is called to create the default `OPTIONS` response.
This can be changed through subclassing to change the default
behaviour of `OPTIONS` responses.
.. versionadded:: 0.7
adapter =
if hasattr(adapter, 'allowed_methods'):
methods = adapter.allowed_methods()
# fallback for Werkzeug < 0.7
methods = []
except MethodNotAllowed, e:
methods = e.valid_methods
except HTTPException, e:
rv = self.response_class()
return rv
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 allowed for `rv`:
.. tabularcolumns:: |p{3.5cm}|p{9.5cm}|
======================= ===========================================
: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 rv is None:
raise ValueError('View function did not return a response')
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 create_url_adapter(self, request):
"""Creates a URL adapter for the given request. The URL adapter
is created at a point where the request context is not yet set up
so the request is passed explicitly.
.. versionadded:: 0.6
return self.url_map.bind_to_environ(request.environ,
def inject_url_defaults(self, endpoint, values):
"""Injects the URL defaults for the given endpoint directly into
the values dictionary passed. This is used internally and
automatically called on URL building.
.. versionadded:: 0.7
funcs = self.url_default_functions.get(None, ())
if '.' in endpoint:
bp = endpoint.split('.', 1)[0]
funcs = chain(funcs, self.url_default_functions.get(bp, ()))
for func in funcs:
func(endpoint, values)
def preprocess_request(self):
"""Called before the actual request dispatching and will
call every as :meth:`before_request` 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.
This also triggers the :meth:`url_value_processor` functions before
the actualy :meth:`before_request` functions are called.
bp =
funcs = self.url_value_preprocessors.get(None, ())
if bp is not None and bp in self.url_value_preprocessors:
funcs = chain(funcs, self.url_value_preprocessors[bp])
for func in funcs:
func(request.endpoint, request.view_args)
funcs = self.before_request_funcs.get(None, ())
if bp is not None and bp in self.before_request_funcs:
funcs = chain(funcs, self.before_request_funcs[bp])
for func in 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. By default this will
call all the :meth:`after_request` decorated functions.
.. versionchanged:: 0.5
As of Flask 0.5 the functions registered for after request
execution are called in reverse order of registration.
:param response: a :attr:`response_class` object.
:return: a new response object or the same, has to be an
instance of :attr:`response_class`.
ctx =
bp = ctx.request.blueprint
if not self.session_interface.is_null_session(ctx.session):
self.save_session(ctx.session, response)
funcs = ()
if bp is not None and bp in self.after_request_funcs:
funcs = reversed(self.after_request_funcs[bp])
if None in self.after_request_funcs:
funcs = chain(funcs, reversed(self.after_request_funcs[None]))
for handler in funcs:
response = handler(response)
return response
def do_teardown_request(self):
"""Called after the actual request dispatching and will
call every as :meth:`teardown_request` decorated function. This is
not actually called by the :class:`Flask` object itself but is always
triggered when the request context is popped. That way we have a
tighter control over certain resources under testing environments.
funcs = reversed(self.teardown_request_funcs.get(None, ()))
bp =
if bp is not None and bp in self.teardown_request_funcs:
funcs = chain(funcs, reversed(self.teardown_request_funcs[bp]))
exc = sys.exc_info()[1]
for func in funcs:
rv = func(exc)
if rv is not None:
return rv
def request_context(self, environ):
"""Creates a :class:`~flask.ctx.RequestContext` 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):
The object returned can also be used without the `with` statement
which is useful for working in the shell. The example above is
doing exactly the same as this code::
ctx = app.request_context(environ)
.. versionchanged:: 0.3
Added support for non-with statement usage and `with` statement
is now passed the ctx object.
:param environ: a WSGI environment
return RequestContext(self, environ)
def test_request_context(self, *args, **kwargs):
"""Creates a WSGI environment from the given values (see
:func:`werkzeug.test.EnvironBuilder` for more information, this
function accepts the same arguments).
from flask.testing import make_test_environ_builder
builder = make_test_environ_builder(self, *args, **kwargs)
return self.request_context(builder.get_environ())
def wsgi_app(self, environ, start_response):
"""The actual WSGI application. This is not implemented in
`__call__` so that middlewares can be applied without losing a
reference to the class. So instead of doing this::
app = MyMiddleware(app)
It's a better idea to do this instead::
app.wsgi_app = MyMiddleware(app.wsgi_app)
Then you still have the original application object around and
can continue to call methods on it.
.. versionchanged:: 0.7
The behavior of the before and after request callbacks was changed
under error conditions and a new callback was added that will
always execute at the end of the request, independent on if an
error ocurred or not. See :ref:`callbacks-and-errors`.
: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):
response = self.full_dispatch_request()
except Exception, e:
response = self.make_response(self.handle_exception(e))
return response(environ, start_response)
def modules(self):
from warnings import warn
warn(DeprecationWarning('Flask.modules is deprecated, use '
'Flask.blueprints instead'), stacklevel=2)
return self.blueprints
def __call__(self, environ, start_response):
"""Shortcut for :attr:`wsgi_app`."""
return self.wsgi_app(environ, start_response)
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