1. Application Object¶

class flask.Flask(import_name, static_path=None, static_url_path=None, static_folder='static', template_folder='templates', instance_path=None, instance_relative_config=False, root_path=None)[source]¶

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 __init__.py file inside) or a standard module (just a .py file).

For more information about resource loading, see open_resource().

Usually you create a Flask instance in your main module or in the __init__.py file of your package like this:

from flask import Flask
app = Flask(__name__)

About the First Parameter

The idea of the first parameter is to give Flask an idea of what belongs to your application. This name is used to find resources on the filesystem, 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/app.py 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 yourapplication.app and not yourapplication.views.frontend)

New in version 0.7: The static_url_path, static_folder, and template_folder parameters were added.

New in version 0.8: The instance_path and instance_relative_config parameters were added.

New in version 0.11: The root_path parameter was added.

Parameters:

import_name – the name of the application package 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. 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. 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 application. 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 path. 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. root_path – Flask by default will automatically calculate the path to the root of the application. In certain situations this cannot be achieved (for instance if the package is a Python 3 namespace package) and needs to be manually defined.

add_template_filter(*args, **kwargs)[source]¶

Register a custom template filter. Works exactly like the template_filter() decorator.

Parameters:	name – the optional name of the filter, otherwise the function name will be used.

add_template_global(*args, **kwargs)[source]¶

Register a custom template global function. Works exactly like the template_global() decorator.

New in version 0.10.

Parameters:	name – the optional name of the global function, otherwise the function name will be used.

add_template_test(*args, **kwargs)[source]¶

Register a custom template test. Works exactly like the template_test() decorator.

New in version 0.10.

Parameters:	name – the optional name of the test, otherwise the function name will be used.

add_url_rule(*args, **kwargs)[source]¶

Connects a URL rule. Works exactly like the route() decorator. If a view_func is provided it will be registered with the endpoint.

Basically this example:

@app.route('/')
def index():
    pass

Is equivalent to the following:

def index():
    pass
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

Internally route() invokes add_url_rule() so if you want to customize the behavior via subclassing you only need to change this method.

For more information refer to URL Route Registrations.

Changed in version 0.2: view_func parameter added.

Changed in version 0.6: OPTIONS is added automatically as method.

Parameters:

rule – the URL rule as string endpoint – the endpoint for the registered URL rule. Flask itself assumes the name of the view function as endpoint view_func – the function to call when serving a request to the provided endpoint options – the options to be forwarded to the underlying 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.

after_request(*args, **kwargs)[source]¶

Register a function to be run after each request.

Your function must take one parameter, an instance of response_class and return a new response object or the same (see process_response()).

As of Flask 0.7 this function might not be executed at the end of the request in case an unhandled exception occurred.

after_request_funcs = None¶

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 close database connections. To register a function here, use the after_request() decorator.

app_context()[source]¶

Binds the application only. For as long as the application is bound to the current context the flask.current_app points to that application. An application context is automatically created when a request context is pushed if necessary.

Example usage:

with app.app_context():
    ...

New in version 0.9.

app_ctx_globals_class¶

The class that is used for the g instance.

Example use cases for a custom class:

1. Store arbitrary attributes on flask.g.
2. Add a property for lazy per-request database connectors.
3. Return None instead of AttributeError on unexpected attributes.
4. Raise exception if an unexpected attr is set, a “controlled” flask.g.

In Flask 0.9 this property was called request_globals_class but it was changed in 0.10 to app_ctx_globals_class because the flask.g object is now application context scoped.

New in version 0.10.

alias of _AppCtxGlobals

auto_find_instance_path()[source]¶

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.

New in version 0.8.

before_first_request(*args, **kwargs)[source]¶

Registers a function to be run before the first request to this instance of the application.

The function will be called without any arguments and its return value is ignored.

New in version 0.8.

before_first_request_funcs = None¶

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 before_first_request() decorator.

New in version 0.8.

before_request(*args, **kwargs)[source]¶

Registers a function to run before each request.

The function will be called without any arguments. If the function returns a non-None value, it’s handled as if it was the return value from the view and further request handling is stopped.

before_request_funcs = None¶

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 before_request() decorator.

blueprints = None¶

all the attached blueprints in a dictionary by name. Blueprints can be attached multiple times so this dictionary does not tell you how often they got attached.

New in version 0.7.

cli = None¶

The click command line context for this application. Commands registered here show up in the flask command once the application has been discovered. The default commands are provided by Flask itself and can be overridden.

This is an instance of a click.Group object.

config = None¶

The configuration dictionary as Config. This behaves exactly like a regular dictionary but supports additional methods to load a config from files.

config_class¶

The class that is used for the config attribute of this app. Defaults to Config.

Example use cases for a custom class:

1. Default values for certain config options.
2. Access to config values through attributes in addition to keys.

New in version 0.11.

alias of Config

context_processor(*args, **kwargs)[source]¶

Registers a template context processor function.

create_global_jinja_loader()[source]¶

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 jinja_loader() function instead.

The global loader dispatches between the loaders of the application and the individual blueprints.

New in version 0.7.

create_jinja_environment()[source]¶

Creates the Jinja2 environment based on jinja_options and select_jinja_autoescape(). Since 0.7 this also adds the Jinja2 globals and filters after initialization. Override this function to customize the behavior.

New in version 0.5.

Changed in version 0.11: Environment.auto_reload set in accordance with TEMPLATES_AUTO_RELOAD configuration option.

create_url_adapter(request)[source]¶

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.

New in version 0.6.

Changed in version 0.9: This can now also be called without a request object when the URL adapter is created for the application context.

debug¶

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 occurs 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.

default_config = ImmutableDict({'JSON_AS_ASCII': True, 'USE_X_SENDFILE': False, 'SESSION_COOKIE_PATH': None, 'SESSION_COOKIE_DOMAIN': None, 'SESSION_COOKIE_NAME': 'session', 'DEBUG': False, 'LOGGER_HANDLER_POLICY': 'always', 'LOGGER_NAME': None, 'SESSION_COOKIE_SECURE': False, 'SECRET_KEY': None, 'EXPLAIN_TEMPLATE_LOADING': False, 'MAX_CONTENT_LENGTH': None, 'PROPAGATE_EXCEPTIONS': None, 'APPLICATION_ROOT': None, 'SERVER_NAME': None, 'PREFERRED_URL_SCHEME': 'http', 'JSONIFY_PRETTYPRINT_REGULAR': True, 'TESTING': False, 'PERMANENT_SESSION_LIFETIME': datetime.timedelta(31), 'TEMPLATES_AUTO_RELOAD': None, 'TRAP_BAD_REQUEST_ERRORS': False, 'JSON_SORT_KEYS': True, 'JSONIFY_MIMETYPE': 'application/json', 'SESSION_COOKIE_HTTPONLY': True, 'SEND_FILE_MAX_AGE_DEFAULT': datetime.timedelta(0, 43200), 'PRESERVE_CONTEXT_ON_EXCEPTION': None, 'SESSION_REFRESH_EACH_REQUEST': True, 'TRAP_HTTP_EXCEPTIONS': False})¶

Default configuration parameters.

dispatch_request()[source]¶

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 make_response().

Changed in version 0.7: This no longer does the exception handling, this code was moved to the new full_dispatch_request().

do_teardown_appcontext(exc=<object object>)[source]¶

Called when an application context is popped. This works pretty much the same as do_teardown_request() but for the application context.

New in version 0.9.

do_teardown_request(exc=<object object>)[source]¶

Called after the actual request dispatching and will call every as teardown_request() decorated function. This is not actually called by the 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.

Changed in version 0.9: Added the exc argument. Previously this was always using the current exception information.

endpoint(*args, **kwargs)[source]¶

A decorator to register a function as an endpoint. Example:

@app.endpoint('example.endpoint')
def example():
    return "example"

Parameters:	endpoint – the name of the endpoint

error_handler_spec = None¶

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 the 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 errorhandler() decorator.

errorhandler(*args, **kwargs)[source]¶

A decorator that is used to register a function give a given error code. Example:

@app.errorhandler(404)
def page_not_found(error):
    return 'This page does not exist', 404

You can also register handlers for arbitrary exceptions:

@app.errorhandler(DatabaseError)
def special_exception_handler(error):
    return 'Database connection failed', 500

You can also register a function as error handler without using the 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 error_handler_spec however is discouraged as it requires fiddling 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.

New in version 0.7: Use register_error_handler() instead of modifying error_handler_spec directly, for application wide error handlers.

New in version 0.7: One can now additionally also register custom exception types that do not necessarily have to be a subclass of the HTTPException class.

Parameters:	code – the code as integer for the handler

extensions = None¶

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 extension module. For example in case of a “Flask-Foo” extension in flask_foo, the key would be 'foo'.

New in version 0.7.

full_dispatch_request()[source]¶

Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling.

New in version 0.7.

get_send_file_max_age(filename)¶

Provides default cache_timeout for the send_file() functions.

By default, this function returns SEND_FILE_MAX_AGE_DEFAULT from the configuration of current_app.

Static file functions such as send_from_directory() use this function, and send_file() calls this function on current_app when the given cache_timeout is None. If a cache_timeout is given in send_file(), that timeout is used; otherwise, this method is called.

This allows subclasses to change the behavior when sending files based on the filename. For example, to set the cache timeout for .js files to 60 seconds:

class MyFlask(flask.Flask):
    def get_send_file_max_age(self, name):
        if name.lower().endswith('.js'):
            return 60
        return flask.Flask.get_send_file_max_age(self, name)

New in version 0.9.

got_first_request¶

This attribute is set to True if the application started handling the first request.

New in version 0.8.

handle_exception(e)[source]¶

Default exception handling that kicks in when an exception occurs 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.

New in version 0.3.

handle_http_exception(e)[source]¶

Handles an HTTP exception. By default this will invoke the registered error handlers and fall back to returning the exception as response.

New in version 0.3.

handle_url_build_error(error, endpoint, values)[source]¶

Handle BuildError on url_for().

handle_user_exception(e)[source]¶

This method is called whenever an exception occurs that should be handled. A special case are HTTPExceptions which are forwarded by this function to the handle_http_exception() method. This function will either return a response value or reraise the exception with the same traceback.

New in version 0.7.

has_static_folder¶

This is True if the package bound object’s container has a folder for static files.

New in version 0.5.

init_jinja_globals()[source]¶

Deprecated. Used to initialize the Jinja2 globals.

New in version 0.5.

Changed in version 0.7: This method is deprecated with 0.7. Override create_jinja_environment() instead.

inject_url_defaults(endpoint, values)[source]¶

Injects the URL defaults for the given endpoint directly into the values dictionary passed. This is used internally and automatically called on URL building.

New in version 0.7.

instance_path = None¶

Holds the path to the instance folder.

New in version 0.8.

iter_blueprints()[source]¶

Iterates over all blueprints by the order they were registered.

New in version 0.11.

jinja_env[source]¶

The Jinja2 environment used to load templates.

jinja_environment¶

The class that is used for the Jinja environment.

New in version 0.11.

alias of Environment

jinja_loader¶

The Jinja loader for this package bound object.

New in version 0.5.

jinja_options = ImmutableDict({'extensions': ['jinja2.ext.autoescape', 'jinja2.ext.with_']})¶

Options that are passed directly to the Jinja2 environment.

json_decoder¶

The JSON decoder class to use. Defaults to JSONDecoder.

New in version 0.10.

alias of JSONDecoder

json_encoder¶

The JSON encoder class to use. Defaults to JSONEncoder.

New in version 0.10.

alias of JSONEncoder

log_exception(exc_info)[source]¶

Logs an exception. This is called by handle_exception() if debugging is disabled and right before the handler is called. The default implementation logs the exception as error on the logger.

New in version 0.8.

logger¶

A 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 occurred (%d apples)', 42)
app.logger.error('An error occurred')

New in version 0.3.

logger_name¶

The name of the logger to use. By default the logger name is the package name passed to the constructor.

New in version 0.4.

make_config(instance_relative=False)[source]¶

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.

New in version 0.8.

make_default_options_response()[source]¶

This method is called to create the default OPTIONS response. This can be changed through subclassing to change the default behavior of OPTIONS responses.

New in version 0.7.

make_null_session()[source]¶

Creates a new instance of a missing session. Instead of overriding this method we recommend replacing the session_interface.

New in version 0.7.

make_response(rv)[source]¶

Converts the return value from a view function to a real response object that is an instance of response_class.

The following types are allowed for rv:

response_class	the object is returned unchanged
str	a response object is created with the string as body
unicode	a response object is created with the string encoded to utf-8 as body
a WSGI function	the function is called as WSGI application and buffered as response object
tuple	A tuple in the form (response, status, headers) or (response, headers) where response is any of the types defined here, status is a string or an integer and headers is a list or a dictionary with header values.

Parameters:	rv – the return value from the view function

Changed in version 0.9: Previously a tuple was interpreted as the arguments for the response object.

make_shell_context()[source]¶

Returns the shell context for an interactive shell for this application. This runs all the registered shell context processors.

New in version 0.11.

name[source]¶

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 overridden to change the value.

New in version 0.8.

open_instance_resource(resource, mode='rb')[source]¶

Opens a resource from the application’s instance folder (instance_path). Otherwise works like open_resource(). Instance resources can also be opened for writing.

Parameters:	resource – the name of the resource. To access resources within subfolders use forward slashes as separator. mode – resource file opening mode, default is ‘rb’.

open_resource(resource, mode='rb')¶

Opens a resource from the application’s resource folder. To see how this works, consider the following folder structure:

/myapplication.py
/schema.sql
/static
    /style.css
/templates
    /layout.html
    /index.html

If you want to open the schema.sql file you would do the following:

with app.open_resource('schema.sql') as f:
    contents = f.read()
    do_something_with(contents)

Parameters:	resource – the name of the resource. To access resources within subfolders use forward slashes as separator. mode – resource file opening mode, default is ‘rb’.

open_session(request)[source]¶

Creates or opens a new session. Default implementation stores all session data in a signed cookie. This requires that the secret_key is set. Instead of overriding this method we recommend replacing the session_interface.

Parameters:	request – an instance of request_class.

permanent_session_lifetime¶

A 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)

preprocess_request()[source]¶

Called before the actual request dispatching and will call each before_request() decorated function, passing no arguments. If any of these functions 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 url_value_processor() functions before the actual before_request() functions are called.

preserve_context_on_exception¶

Returns the value of the PRESERVE_CONTEXT_ON_EXCEPTION configuration value in case it’s set, otherwise a sensible default is returned.

New in version 0.7.

process_response(response)[source]¶

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 after_request() decorated functions.

Changed in version 0.5: As of Flask 0.5 the functions registered for after request execution are called in reverse order of registration.

Parameters:	response – a response_class object.
Returns:	a new response object or the same, has to be an instance of response_class.

propagate_exceptions¶

Returns the value of the PROPAGATE_EXCEPTIONS configuration value in case it’s set, otherwise a sensible default is returned.

New in version 0.7.

register_blueprint(*args, **kwargs)[source]¶

Register a blueprint on the application. For information about blueprints head over to Modular Applications with Blueprints.

The blueprint name is passed in as the first argument. Options are passed as additional keyword arguments and forwarded to blueprints in an “options” dictionary.

Parameters:

subdomain – set a subdomain for the blueprint url_prefix – set the prefix for all URLs defined on the blueprint. (url_prefix='/<lang code>') url_defaults – a dictionary with URL defaults that is added to each and every URL defined with this blueprint static_folder – add a static folder to urls in this blueprint static_url_path – add a static url path to urls in this blueprint template_folder – set an alternate template folder root_path – set an alternate root path for this blueprint

New in version 0.7.

register_error_handler(code_or_exception, f)[source]¶

Alternative error attach function to the errorhandler() decorator that is more straightforward to use for non decorator usage.

New in version 0.7.

request_class¶

The class that is used for request objects. See Request for more information.

alias of Request

request_context(environ)[source]¶

Creates a 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):
    do_something_with(request)

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)
ctx.push()
try:
    do_something_with(request)
finally:
    ctx.pop()

Changed in version 0.3: Added support for non-with statement usage and with statement is now passed the ctx object.

Parameters:	environ – a WSGI environment

response_class¶

The class that is used for response objects. See Response for more information.

alias of Response

route(rule, **options)[source]¶

A decorator that is used to register a view function for a given URL rule. This does the same thing as add_url_rule() but is intended for decorator usage:

@app.route('/')
def index():
    return 'Hello World'

For more information refer to URL Route Registrations.

Parameters:

rule – the URL rule as string endpoint – the endpoint for the registered URL rule. Flask itself assumes the name of the view function as endpoint options – the options to be forwarded to the underlying 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.

run(host=None, port=None, debug=None, **options)[source]¶

Runs the application on a local development server.

Do not use run() in a production setting. It is not intended to meet security and performance requirements for a production server. Instead, see Application Deployment for WSGI server recommendations.

If the 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.

It is not recommended to use this function for development with automatic reloading as this is badly supported. Instead you should be using the flask command line script’s run support.

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 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 catch.

Changed in version 0.10: The default port is now picked from the SERVER_NAME variable.

Parameters:

host – the hostname to listen on. Set this to '0.0.0.0' to have the server available externally as well. Defaults to '127.0.0.1'. port – the port of the webserver. Defaults to 5000 or the port defined in the SERVER_NAME config variable if present. debug – if given, enable or disable debug mode. See debug. options – the options to be forwarded to the underlying Werkzeug server. See werkzeug.serving.run_simple() for more information.

save_session(session, response)[source]¶

Saves the session if it needs updates. For the default implementation, check open_session(). Instead of overriding this method we recommend replacing the session_interface.

Parameters:	session – the session to be saved (a SecureCookie object) response – an instance of response_class

secret_key¶

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.

select_jinja_autoescape(filename)[source]¶

Returns True if autoescaping should be active for the given template name. If no template name is given, returns True.

New in version 0.5.

send_file_max_age_default¶

A timedelta which is used as default cache_timeout for the send_file() functions. The default is 12 hours.

This attribute can also be configured from the config with the SEND_FILE_MAX_AGE_DEFAULT configuration key. This configuration variable can also be set with an integer value used as seconds. Defaults to timedelta(hours=12)

send_static_file(filename)¶

Function used internally to send static files from the static folder to the browser.

New in version 0.5.

session_cookie_name¶

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_interface = <flask.sessions.SecureCookieSessionInterface object>¶

the session interface to use. By default an instance of SecureCookieSessionInterface is used here.

New in version 0.8.

shell_context_processor(*args, **kwargs)[source]¶

Registers a shell context processor function.

New in version 0.11.

shell_context_processors = None¶

A list of shell context processor functions that should be run when a shell context is created.

New in version 0.11.

should_ignore_error(error)[source]¶

This is called to figure out if an error should be ignored or not as far as the teardown system is concerned. If this function returns True then the teardown handlers will not be passed the error.

New in version 0.10.

static_folder¶

The absolute path to the configured static folder.

teardown_appcontext(*args, **kwargs)[source]¶

Registers a function to be called when the application context ends. These functions are typically also called when the request context is popped.

Example:

ctx = app.app_context()
ctx.push()
...
ctx.pop()

When ctx.pop() is executed in the above example, the teardown functions are called just before the app context moves from the stack of active contexts. This becomes relevant if you are using such constructs in tests.

Since a request context typically also manages an application context it would also be called when you pop a request context.

When a teardown function was called because of an exception it will be passed an error object.

The return values of teardown functions are ignored.

New in version 0.9.

teardown_appcontext_funcs = None¶

A list of functions that are called when the application context is destroyed. Since the application context is also torn down if the request ends this is the place to store code that disconnects from databases.

New in version 0.9.

teardown_request(*args, **kwargs)[source]¶

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.

Example:

ctx = app.test_request_context()
ctx.push()
...
ctx.pop()

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 necessary 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 occurring errors.

When a teardown function was called because of a exception it will be passed an error object.

The return values of teardown functions are ignored.

Debug Note

In debug mode Flask will not tear down a request on an exception immediately. Instead it will keep it alive so that the interactive debugger can still access it. This behavior can be controlled by the PRESERVE_CONTEXT_ON_EXCEPTION configuration variable.

teardown_request_funcs = None¶

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 teardown_request() decorator.

New in version 0.7.

template_context_processors = None¶

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 context_processor() decorator.

template_filter(*args, **kwargs)[source]¶

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:

@app.template_filter()
def reverse(s):
    return s[::-1]

Parameters:	name – the optional name of the filter, otherwise the function name will be used.

template_global(*args, **kwargs)[source]¶

A decorator that is used to register a custom template global function. You can specify a name for the global function, otherwise the function name will be used. Example:

@app.template_global()
def double(n):
    return 2 * n

New in version 0.10.

Parameters:	name – the optional name of the global function, otherwise the function name will be used.

template_test(*args, **kwargs)[source]¶

A decorator that is used to register custom template test. You can specify a name for the test, otherwise the function name will be used. Example:

@app.template_test()
def is_prime(n):
    if n == 2:
        return True
    for i in range(2, int(math.ceil(math.sqrt(n))) + 1):
        if n % i == 0:
            return False
    return True

New in version 0.10.

Parameters:	name – the optional name of the test, otherwise the function name will be used.

test_client(use_cookies=True, **kwargs)[source]¶

Creates a test client for this application. For information about unit testing head over to 1   Testing Flask Applications.

Note that if you are testing for assertions or exceptions in your application code, you must set app.testing = True in order for the exceptions to propagate to the test client. Otherwise, the exception will be handled by the application (not visible to the test client) and the only indication of an AssertionError or other exception will be a 500 status code response to the test client. See the testing attribute. For example:

app.testing = True
client = app.test_client()

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'

Additionally, you may pass optional keyword arguments that will then be passed to the application’s test_client_class constructor. For example:

from flask.testing import FlaskClient

class CustomClient(FlaskClient):
    def __init__(self, authentication=None, *args, **kwargs):
        FlaskClient.__init__(*args, **kwargs)
        self._authentication = authentication

app.test_client_class = CustomClient
client = app.test_client(authentication='Basic ....')

See FlaskClient for more information.

Changed in version 0.4: added support for with block usage for the client.

New in version 0.7: The use_cookies parameter was added as well as the ability to override the client to be used by setting the test_client_class attribute.

Changed in version 0.11: Added **kwargs to support passing additional keyword arguments to the constructor of test_client_class.

test_client_class = None¶

the test client that is used with when test_client is used.

New in version 0.7.

test_request_context(*args, **kwargs)[source]¶

Creates a WSGI environment from the given values (see werkzeug.test.EnvironBuilder for more information, this function accepts the same arguments).

testing¶

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.

trap_http_exception(e)[source]¶

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 exceptions.

New in version 0.8.

update_template_context(context)[source]¶

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 overridden if a context processor decides to return a value with the same key.

Parameters:	context – the context as a dictionary that is updated in place to add extra variables.

url_build_error_handlers = None¶

A list of functions that are called when url_for() raises a BuildError. Each function registered here is called with error, endpoint and values. If a function returns None or raises a BuildError the next function is tried.

New in version 0.9.

url_default_functions = None¶

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 url_defaults() function that adds the parameters automatically again that were removed that way.

New in version 0.7.

url_defaults(*args, **kwargs)[source]¶

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.

url_map = None¶

The 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

url_rule_class¶

The rule object to use for URL rules created. This is used by add_url_rule(). Defaults to werkzeug.routing.Rule.

New in version 0.7.

alias of Rule

url_value_preprocessor(*args, **kwargs)[source]¶

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.

url_value_preprocessors = None¶

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

New in version 0.7.

use_x_sendfile¶

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 send_file() method.

New in version 0.2.

This attribute can also be configured from the config with the USE_X_SENDFILE configuration key. Defaults to False.

view_functions = None¶

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 route() decorator.

wsgi_app(environ, start_response)[source]¶

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.

Changed in version 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 occurred or not. See Callbacks and Errors.

Parameters:	environ – a WSGI environment start_response – a callable accepting a status code, a list of headers and an optional exception context to start the response