class flask.Flask(import_name, static_url_path=None, static_folder='static', static_host=None, host_matching=False, subdomain_matching=False, template_folder='templates', instance_path=None, instance_relative_config=False, root_path=None)  
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)   Changelog New in version 1.0: The host_matching and static_host parameters were added.   New in version 1.0: The subdomain_matching parameter was added. Subdomain matching needs to be enabled manually now. Setting SERVER_NAME does not implicitly enable it.   New in version 0.11: The root_path parameter was added.   New in version 0.8: The instance_path and instance_relative_config parameters were added.   New in version 0.7: The static_url_path, static_folder, and template_folder parameters were added.   Parameters 
 
import_name (str) – the name of the application package 
static_url_path (Optional[str]) – 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 (Optional[str]) – The folder with static files that is served at static_url_path. Relative to the application root_path or an absolute path. Defaults to 'static'. 
static_host (Optional[str]) – the host to use when adding the static route. Defaults to None. Required when using host_matching=True with a static_folder configured. 
host_matching (bool) – set url_map.host_matching attribute. Defaults to False. 
subdomain_matching (bool) – consider the subdomain relative to SERVER_NAME when matching routes. Defaults to False. 
template_folder (Optional[str]) – 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 (Optional[str]) – 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 (bool) – 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 (Optional[str]) – The path to the root of the application files. This should only be set manually when it can’t be detected automatically, such as for namespace packages.     
add_template_filter(f, name=None)  
Register a custom template filter. Works exactly like the template_filter() decorator.  Parameters 
 
name (Optional[str]) – the optional name of the filter, otherwise the function name will be used. 
f (Callable[[Any], str]) –    Return type 
None   
  
add_template_global(f, name=None)  
Register a custom template global function. Works exactly like the template_global() decorator.  Changelog New in version 0.10.   Parameters 
 
name (Optional[str]) – the optional name of the global function, otherwise the function name will be used. 
f (Callable[[], Any]) –    Return type 
None   
  
add_template_test(f, name=None)  
Register a custom template test. Works exactly like the template_test() decorator.  Changelog New in version 0.10.   Parameters 
 
name (Optional[str]) – the optional name of the test, otherwise the function name will be used. 
f (Callable[[Any], bool]) –    Return type 
None   
  
add_url_rule(rule, endpoint=None, view_func=None, provide_automatic_options=None, **options)  
Register a rule for routing incoming requests and building URLs. The route() decorator is a shortcut to call this with the view_func argument. These are equivalent: @app.route("/")
def index():
    ...
 def index():
    ...

app.add_url_rule("/", view_func=index)
 See URL Route Registrations. The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed. An error will be raised if a function has already been registered for the endpoint. The methods parameter defaults to ["GET"]. HEAD is always added automatically, and OPTIONS is added automatically by default. view_func does not necessarily need to be passed, but if the rule should participate in routing an endpoint name must be associated with a view function at some point with the endpoint() decorator. app.add_url_rule("/", endpoint="index")

@app.endpoint("index")
def index():
    ...
 If view_func has a required_methods attribute, those methods are added to the passed and automatic methods. If it has a provide_automatic_methods attribute, it is used as the default if the parameter is not passed.  Parameters 
 
rule (str) – The URL rule string. 
endpoint (Optional[str]) – The endpoint name to associate with the rule and view function. Used when routing and building URLs. Defaults to view_func.__name__. 
view_func (Optional[Callable]) – The view function to associate with the endpoint name. 
provide_automatic_options (Optional[bool]) – Add the OPTIONS method and respond to OPTIONS requests automatically. 
options (Any) – Extra options passed to the Rule object.   Return type 
None   
  
after_request(f)  
Register a function to run after each request to this object. The function is called with the response object, and must return a response object. This allows the functions to modify or replace the response before it is sent. If a function raises an exception, any remaining after_request functions will not be called. Therefore, this should not be used for actions that must execute, such as to close resources. Use teardown_request() for that.  Parameters 
f (Callable[[Response], Response]) –   Return type 
Callable[[Response], Response]   
  
after_request_funcs: t.Dict[AppOrBlueprintKey, t.List[AfterRequestCallable]]  
A data structure of functions to call at the end of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests. To register a function, use the after_request() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
app_context()  
Create an AppContext. Use as a with block to push the context, which will make current_app point at this application. An application context is automatically pushed by RequestContext.push() when handling a request, and when running a CLI command. Use this to manually create a context outside of these situations. with app.app_context():
    init_db()
 See The Application Context.  Changelog New in version 0.9.   Return type 
flask.ctx.AppContext   
  
app_ctx_globals_class  
alias of flask.ctx._AppCtxGlobals 
  
async_to_sync(func)  
Return a sync function that will run the coroutine function. result = app.async_to_sync(func)(*args, **kwargs)
 Override this method to change how the app converts async code to be synchronously callable.  New in version 2.0.   Parameters 
func (Callable[[...], Coroutine]) –   Return type 
Callable[[…], Any]   
  
auto_find_instance_path()  
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.  Changelog New in version 0.8.   Return type 
str   
  
before_first_request(f)  
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.  Changelog New in version 0.8.   Parameters 
f (Callable[[], None]) –   Return type 
Callable[[], None]   
  
before_first_request_funcs: t.List[BeforeRequestCallable]  
A list of functions that will be called at the beginning of the first request to this instance. To register a function, use the before_first_request() decorator.  Changelog New in version 0.8.  

  
before_request(f)  
Register a function to run before each request. For example, this can be used to open a database connection, or to load the logged in user from the session. @app.before_request
def load_user():
    if "user_id" in session:
        g.user = db.session.get(session["user_id"])
 The function will be called without any arguments. If it returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.  Parameters 
f (Callable[[], None]) –   Return type 
Callable[[], None]   
  
before_request_funcs: t.Dict[AppOrBlueprintKey, t.List[BeforeRequestCallable]]  
A data structure of functions to call at the beginning of each request, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests. To register a function, use the before_request() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
blueprints: t.Dict[str, ‘Blueprint’]  
Maps registered blueprint names to blueprint objects. The dict retains the order the blueprints were registered in. Blueprints can be registered multiple times, this dict does not track how often they were attached.  Changelog New in version 0.7.  

  
cli  
The Click command group for registering CLI commands for this object. The commands are available from the flask command once the application has been discovered and blueprints have been registered. 
  
config  
The configuration dictionary as Config. This behaves exactly like a regular dictionary but supports additional methods to load a config from files. 
  
config_class  
alias of flask.config.Config 
  
context_processor(f)  
Registers a template context processor function.  Parameters 
f (Callable[[], Dict[str, Any]]) –   Return type 
Callable[[], Dict[str, Any]]   
  
create_global_jinja_loader()  
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.  Changelog New in version 0.7.   Return type 
flask.templating.DispatchingJinjaLoader   
  
create_jinja_environment()  
Create the Jinja environment based on jinja_options and the various Jinja-related methods of the app. Changing jinja_options after this will have no effect. Also adds Flask-related globals and filters to the environment.  Changelog Changed in version 0.11: Environment.auto_reload set in accordance with TEMPLATES_AUTO_RELOAD configuration option.   New in version 0.5.   Return type 
flask.templating.Environment   
  
create_url_adapter(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.  Changelog Changed in version 1.0: SERVER_NAME no longer implicitly enables subdomain matching. Use subdomain_matching instead.   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.   New in version 0.6.   Parameters 
request (Optional[flask.wrappers.Request]) –   Return type 
Optional[werkzeug.routing.MapAdapter]   
  
property debug: bool  
Whether debug mode is enabled. When using flask run to start the development server, an interactive debugger will be shown for unhandled exceptions, and the server will be reloaded when code changes. This maps to the DEBUG config key. This is enabled when env is 'development' and is overridden by the FLASK_DEBUG environment variable. It may not behave as expected if set in code. Do not enable debug mode when deploying in production. Default: True if env is 'development', or False otherwise. 
  
default_config = {'APPLICATION_ROOT': '/', 'DEBUG': None, 'ENV': None, 'EXPLAIN_TEMPLATE_LOADING': False, 'JSONIFY_MIMETYPE': 'application/json', 'JSONIFY_PRETTYPRINT_REGULAR': False, 'JSON_AS_ASCII': True, 'JSON_SORT_KEYS': True, 'MAX_CONTENT_LENGTH': None, 'MAX_COOKIE_SIZE': 4093, 'PERMANENT_SESSION_LIFETIME': datetime.timedelta(days=31), 'PREFERRED_URL_SCHEME': 'http', 'PRESERVE_CONTEXT_ON_EXCEPTION': None, 'PROPAGATE_EXCEPTIONS': None, 'SECRET_KEY': None, 'SEND_FILE_MAX_AGE_DEFAULT': None, 'SERVER_NAME': None, 'SESSION_COOKIE_DOMAIN': None, 'SESSION_COOKIE_HTTPONLY': True, 'SESSION_COOKIE_NAME': 'session', 'SESSION_COOKIE_PATH': None, 'SESSION_COOKIE_SAMESITE': None, 'SESSION_COOKIE_SECURE': False, 'SESSION_REFRESH_EACH_REQUEST': True, 'TEMPLATES_AUTO_RELOAD': None, 'TESTING': False, 'TRAP_BAD_REQUEST_ERRORS': None, 'TRAP_HTTP_EXCEPTIONS': False, 'USE_X_SENDFILE': False}  
Default configuration parameters. 
  
delete(rule, **options)  
Shortcut for route() with methods=["DELETE"].  New in version 2.0.   Parameters 
 
rule (str) –  
options (Any) –    Return type 
Callable   
  
dispatch_request()  
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().  Changelog Changed in version 0.7: This no longer does the exception handling, this code was moved to the new full_dispatch_request().   Return type 
Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], WSGIApplication]   
  
do_teardown_appcontext(exc=<object object>)  
Called right before the application context is popped. When handling a request, the application context is popped after the request context. See do_teardown_request(). This calls all functions decorated with teardown_appcontext(). Then the appcontext_tearing_down signal is sent. This is called by AppContext.pop().  Changelog New in version 0.9.   Parameters 
exc (Optional[BaseException]) –   Return type 
None   
  
do_teardown_request(exc=<object object>)  
Called after the request is dispatched and the response is returned, right before the request context is popped. This calls all functions decorated with teardown_request(), and Blueprint.teardown_request() if a blueprint handled the request. Finally, the request_tearing_down signal is sent. This is called by RequestContext.pop(), which may be delayed during testing to maintain access to resources.  Parameters 
exc (Optional[BaseException]) – An unhandled exception raised while dispatching the request. Detected from the current exception information if not passed. Passed to each teardown function.  Return type 
None    Changelog Changed in version 0.9: Added the exc argument.  

  
endpoint(endpoint)  
Decorate a view function to register it for the given endpoint. Used if a rule is added without a view_func with add_url_rule(). app.add_url_rule("/ex", endpoint="example")

@app.endpoint("example")
def example():
    ...
  Parameters 
endpoint (str) – The endpoint name to associate with the view function.  Return type 
Callable   
  
ensure_sync(func)  
Ensure that the function is synchronous for WSGI workers. Plain def functions are returned as-is. async def functions are wrapped to run and wait for the response. Override this method to change how the app runs async views.  New in version 2.0.   Parameters 
func (Callable) –   Return type 
Callable   
  
env  
What environment the app is running in. Flask and extensions may enable behaviors based on the environment, such as enabling debug mode. This maps to the ENV config key. This is set by the FLASK_ENV environment variable and may not behave as expected if set in code. Do not enable development when deploying in production. Default: 'production' 
  
error_handler_spec: t.Dict[AppOrBlueprintKey, t.Dict[t.Optional[int], t.Dict[t.Type[Exception], ErrorHandlerCallable]]]  
A data structure of registered error handlers, in the format {scope: {code: {class: handler}}}`. The scope key is the name of a blueprint the handlers are active for, or None for all requests. The code key is the HTTP status code for HTTPException, or None for other exceptions. The innermost dictionary maps exception classes to handler functions. To register an error handler, use the errorhandler() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
errorhandler(code_or_exception)  
Register a function to handle errors by code or exception class. A decorator that is used to register a function given an 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
  Changelog 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_or_exception (Union[Type[Exception], int]) – the code as integer for the handler, or an arbitrary exception  Return type 
Callable   
  
extensions: dict  
a place where extensions can store application specific state. For example this is where an extension could store database engines and similar things. 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'.  Changelog New in version 0.7.  

  
full_dispatch_request()  
Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling.  Changelog New in version 0.7.   Return type 
flask.wrappers.Response   
  
get(rule, **options)  
Shortcut for route() with methods=["GET"].  New in version 2.0.   Parameters 
 
rule (str) –  
options (Any) –    Return type 
Callable   
  
get_send_file_max_age(filename)  
Used by send_file() to determine the max_age cache value for a given file path if it wasn’t passed. By default, this returns SEND_FILE_MAX_AGE_DEFAULT from the configuration of current_app. This defaults to None, which tells the browser to use conditional requests instead of a timed cache, which is usually preferable.  Changed in version 2.0: The default configuration is None instead of 12 hours.   Changelog New in version 0.9.   Parameters 
filename (str) –   Return type 
Optional[int]   
  
property got_first_request: bool  
This attribute is set to True if the application started handling the first request.  Changelog New in version 0.8.  

  
handle_exception(e)  
Handle an exception that did not have an error handler associated with it, or that was raised from an error handler. This always causes a 500 InternalServerError. Always sends the got_request_exception signal. If propagate_exceptions is True, such as in debug mode, the error will be re-raised so that the debugger can display it. Otherwise, the original exception is logged, and an InternalServerError is returned. If an error handler is registered for InternalServerError or 500, it will be used. For consistency, the handler will always receive the InternalServerError. The original unhandled exception is available as e.original_exception.  Changelog Changed in version 1.1.0: Always passes the InternalServerError instance to the handler, setting original_exception to the unhandled error.   Changed in version 1.1.0: after_request functions and other finalization is done even for the default 500 response when there is no handler.   New in version 0.3.   Parameters 
e (Exception) –   Return type 
flask.wrappers.Response   
  
handle_http_exception(e)  
Handles an HTTP exception. By default this will invoke the registered error handlers and fall back to returning the exception as response.  Changelog Changed in version 1.0.3: RoutingException, used internally for actions such as slash redirects during routing, is not passed to error handlers.   Changed in version 1.0: Exceptions are looked up by code and by MRO, so HTTPExcpetion subclasses can be handled with a catch-all handler for the base HTTPException.   New in version 0.3.   Parameters 
e (werkzeug.exceptions.HTTPException) –   Return type 
Union[werkzeug.exceptions.HTTPException, Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], WSGIApplication]   
  
handle_url_build_error(error, endpoint, values)  
Handle BuildError on url_for().  Parameters 
 
error (Exception) –  
endpoint (str) –  
values (dict) –    Return type 
str   
  
handle_user_exception(e)  
This method is called whenever an exception occurs that should be handled. A special case is HTTPException which is forwarded to the handle_http_exception() method. This function will either return a response value or reraise the exception with the same traceback.  Changelog Changed in version 1.0: Key errors raised from request data like form show the bad key in debug mode rather than a generic bad request message.   New in version 0.7.   Parameters 
e (Exception) –   Return type 
Union[werkzeug.exceptions.HTTPException, Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], WSGIApplication]   
  
property has_static_folder: bool  
True if static_folder is set.  Changelog New in version 0.5.  

  
import_name  
The name of the package or module that this object belongs to. Do not change this once it is set by the constructor. 
  
inject_url_defaults(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.  Changelog New in version 0.7.   Parameters 
 
endpoint (str) –  
values (dict) –    Return type 
None   
  
instance_path  
Holds the path to the instance folder.  Changelog New in version 0.8.  

  
iter_blueprints()  
Iterates over all blueprints by the order they were registered.  Changelog New in version 0.11.   Return type 
ValuesView[Blueprint]   
  
property jinja_env: flask.templating.Environment  
The Jinja environment used to load templates. The environment is created the first time this property is accessed. Changing jinja_options after that will have no effect. 
  
jinja_environment  
alias of flask.templating.Environment 
  
property jinja_loader: Optional[jinja2.loaders.FileSystemLoader]  
The Jinja loader for this object’s templates. By default this is a class jinja2.loaders.FileSystemLoader to template_folder if it is set.  Changelog New in version 0.5.  

  
jinja_options: dict = {}  
Options that are passed to the Jinja environment in create_jinja_environment(). Changing these options after the environment is created (accessing jinja_env) will have no effect.  Changelog Changed in version 1.1.0: This is a dict instead of an ImmutableDict to allow easier configuration.  

  
json_decoder  
alias of flask.json.JSONDecoder 
  
json_encoder  
alias of flask.json.JSONEncoder 
  
log_exception(exc_info)  
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.  Changelog New in version 0.8.   Parameters 
exc_info (Union[Tuple[type, BaseException, types.TracebackType], Tuple[None, None, None]]) –   Return type 
None   
  
property logger: logging.Logger  
A standard Python Logger for the app, with the same name as name. In debug mode, the logger’s level will be set to DEBUG. If there are no handlers configured, a default handler will be added. See Logging for more information.  Changelog Changed in version 1.1.0: The logger takes the same name as name rather than hard-coding "flask.app".   Changed in version 1.0.0: Behavior was simplified. The logger is always named "flask.app". The level is only set during configuration, it doesn’t check app.debug each time. Only one format is used, not different ones depending on app.debug. No handlers are removed, and a handler is only added if no handlers are already configured.   New in version 0.3.  

  
make_config(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.  Changelog New in version 0.8.   Parameters 
instance_relative (bool) –   Return type 
flask.config.Config   
  
make_default_options_response()  
This method is called to create the default OPTIONS response. This can be changed through subclassing to change the default behavior of OPTIONS responses.  Changelog New in version 0.7.   Return type 
flask.wrappers.Response   
  
make_response(rv)  
Convert the return value from a view function to an instance of response_class.  Parameters 
rv (Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]) – 
the return value from the view function. The view function must return a response. Returning None, or the view ending without returning, is not allowed. The following types are allowed for view_rv:  
str 

A response object is created with the string encoded to UTF-8 as the body.  
bytes 

A response object is created with the bytes as the body.  
dict 

A dictionary that will be jsonify’d before being returned.  
tuple 

Either (body, status, headers), (body, status), or (body, headers), where body is any of the other types allowed here, status is a string or an integer, and headers is a dictionary or a list of (key, value) tuples. If body is a response_class instance, status overwrites the exiting value and headers are extended.  
response_class


The object is returned unchanged.  
other Response class 

The object is coerced to response_class.  
callable()


The function is called as a WSGI application. The result is used to create a response object.    Return type 
flask.wrappers.Response    Changelog Changed in version 0.9: Previously a tuple was interpreted as the arguments for the response object.  

  
make_shell_context()  
Returns the shell context for an interactive shell for this application. This runs all the registered shell context processors.  Changelog New in version 0.11.   Return type 
dict   
  
property name: str  
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.  Changelog New in version 0.8.  

  
open_instance_resource(resource, mode='rb')  
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 (str) – the name of the resource. To access resources within subfolders use forward slashes as separator. 
mode (str) – resource file opening mode, default is ‘rb’.   Return type 
IO   
  
open_resource(resource, mode='rb')  
Open a resource file relative to root_path for reading. For example, if the file schema.sql is next to the file app.py where the Flask app is defined, it can be opened with: with app.open_resource("schema.sql") as f:
    conn.executescript(f.read())
  Parameters 
 
resource (str) – Path to the resource relative to root_path. 
mode (str) – Open the file in this mode. Only reading is supported, valid values are “r” (or “rt”) and “rb”.   Return type 
IO   
  
patch(rule, **options)  
Shortcut for route() with methods=["PATCH"].  New in version 2.0.   Parameters 
 
rule (str) –  
options (Any) –    Return type 
Callable   
  
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) 
  
post(rule, **options)  
Shortcut for route() with methods=["POST"].  New in version 2.0.   Parameters 
 
rule (str) –  
options (Any) –    Return type 
Callable   
  
preprocess_request()  
Called before the request is dispatched. Calls url_value_preprocessors registered with the app and the current blueprint (if any). Then calls before_request_funcs registered with the app and the blueprint. If any before_request() handler returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.  Return type 
Optional[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, …]]], List[Tuple[str, Union[str, List[str], Tuple[str, …]]]]]], WSGIApplication]]   
  
property preserve_context_on_exception: bool  
Returns the value of the PRESERVE_CONTEXT_ON_EXCEPTION configuration value in case it’s set, otherwise a sensible default is returned.  Changelog New in version 0.7.  

  
process_response(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 after_request() decorated functions.  Changelog 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 (flask.wrappers.Response) – a response_class object.  Returns 
a new response object or the same, has to be an instance of response_class.  Return type 
flask.wrappers.Response   
  
property propagate_exceptions: bool  
Returns the value of the PROPAGATE_EXCEPTIONS configuration value in case it’s set, otherwise a sensible default is returned.  Changelog New in version 0.7.  

  
put(rule, **options)  
Shortcut for route() with methods=["PUT"].  New in version 2.0.   Parameters 
 
rule (str) –  
options (Any) –    Return type 
Callable   
  
register_blueprint(blueprint, **options)  
Register a Blueprint on the application. Keyword arguments passed to this method will override the defaults set on the blueprint. Calls the blueprint’s register() method after recording the blueprint in the application’s blueprints.  Parameters 
 
blueprint (Blueprint) – The blueprint to register. 
url_prefix – Blueprint routes will be prefixed with this. 
subdomain – Blueprint routes will match on this subdomain. 
url_defaults – Blueprint routes will use these default values for view arguments. 
options (Any) – Additional keyword arguments are passed to BlueprintSetupState. They can be accessed in record() callbacks.   Return type 
None    Changelog New in version 0.7.  

  
register_error_handler(code_or_exception, f)  
Alternative error attach function to the errorhandler() decorator that is more straightforward to use for non decorator usage.  Changelog New in version 0.7.   Parameters 
 
code_or_exception (Union[Type[Exception], int]) –  
f (Callable[[Exception], Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int], Tuple[Union[Response, AnyStr, Dict[str, Any], Generator[AnyStr, None, None]], int, Union[Headers, Dict[str, Union[str, List[str], Tuple[str, ...]]], List[Tuple[str, Union[str, List[str], Tuple[str, ...]]]]]], WSGIApplication]]) –    Return type 
None   
  
request_class  
alias of flask.wrappers.Request 
  
request_context(environ)  
Create a RequestContext representing a WSGI environment. Use a with block to push the context, which will make request point at this request. See The Request Context. Typically you should not call this from your own code. A request context is automatically pushed by the wsgi_app() when handling a request. Use test_request_context() to create an environment and context instead of this method.  Parameters 
environ (dict) – a WSGI environment  Return type 
flask.ctx.RequestContext   
  
response_class  
alias of flask.wrappers.Response 
  
root_path  
Absolute path to the package on the filesystem. Used to look up resources contained in the package. 
  
route(rule, **options)  
Decorate a view function to register it with the given URL rule and options. Calls add_url_rule(), which has more details about the implementation. @app.route("/")
def index():
    return "Hello, World!"
 See URL Route Registrations. The endpoint name for the route defaults to the name of the view function if the endpoint parameter isn’t passed. The methods parameter defaults to ["GET"]. HEAD and OPTIONS are added automatically.  Parameters 
 
rule (str) – The URL rule string. 
options (Any) – Extra options passed to the Rule object.   Return type 
Callable   
  
run(host=None, port=None, debug=None, load_dotenv=True, **options)  
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 Deployment Options 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.   Parameters 
 
host (Optional[str]) – 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' or the host in the SERVER_NAME config variable if present. 
port (Optional[int]) – the port of the webserver. Defaults to 5000 or the port defined in the SERVER_NAME config variable if present. 
debug (Optional[bool]) – if given, enable or disable debug mode. See debug. 
load_dotenv (bool) – Load the nearest .env and .flaskenv files to set environment variables. Will also change the working directory to the directory containing the first file found. 
options (Any) – the options to be forwarded to the underlying Werkzeug server. See werkzeug.serving.run_simple() for more information.   Return type 
None    Changelog Changed in version 1.0: If installed, python-dotenv will be used to load environment variables from .env and .flaskenv files. If set, the FLASK_ENV and FLASK_DEBUG environment variables will override env and debug. Threaded mode is enabled by default.   Changed in version 0.10: The default port is now picked from the SERVER_NAME variable.  

  
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)  
Returns True if autoescaping should be active for the given template name. If no template name is given, returns True.  Changelog New in version 0.5.   Parameters 
filename (str) –   Return type 
bool   
  
send_file_max_age_default  
A timedelta or number of seconds which is used as the default max_age for send_file(). The default is None, which tells the browser to use conditional requests instead of a timed cache. Configured with the SEND_FILE_MAX_AGE_DEFAULT configuration key.  Changed in version 2.0: Defaults to None instead of 12 hours.  
  
send_static_file(filename)  
The view function used to serve files from static_folder. A route is automatically registered for this view at static_url_path if static_folder is set.  Changelog New in version 0.5.   Parameters 
filename (str) –   Return type 
Response   
  
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.  Changelog New in version 0.8.  

  
shell_context_processor(f)  
Registers a shell context processor function.  Changelog New in version 0.11.   Parameters 
f (Callable) –   Return type 
Callable   
  
shell_context_processors: t.List[t.Callable[], t.Dict[str, t.Any]]]  
A list of shell context processor functions that should be run when a shell context is created.  Changelog New in version 0.11.  

  
should_ignore_error(error)  
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.  Changelog New in version 0.10.   Parameters 
error (Optional[BaseException]) –   Return type 
bool   
  
property static_folder: Optional[str]  
The absolute path to the configured static folder. None if no static folder is set. 
  
property static_url_path: Optional[str]  
The URL prefix that the static route will be accessible from. If it was not configured during init, it is derived from static_folder. 
  
teardown_appcontext(f)  
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 unhandled exception it will be passed an error object. If an errorhandler() is registered, it will handle the exception and the teardown will not receive it. The return values of teardown functions are ignored.  Changelog New in version 0.9.   Parameters 
f (Callable[[Optional[BaseException]], flask.wrappers.Response]) –   Return type 
Callable[[Optional[BaseException]], flask.wrappers.Response]   
  
teardown_appcontext_funcs: t.List[TeardownCallable]  
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.  Changelog New in version 0.9.  

  
teardown_request(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. 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. Teardown functions must avoid raising exceptions, since they . If they 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 an 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.   Parameters 
f (Callable[[Optional[BaseException]], Response]) –   Return type 
Callable[[Optional[BaseException]], Response]   
  
teardown_request_funcs: t.Dict[AppOrBlueprintKey, t.List[TeardownCallable]]  
A data structure of functions to call at the end of each request even if an exception is raised, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests. To register a function, use the teardown_request() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
template_context_processors: t.Dict[AppOrBlueprintKey, t.List[TemplateContextProcessorCallable]]  
A data structure of functions to call to pass extra context values when rendering templates, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests. To register a function, use the context_processor() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
template_filter(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: @app.template_filter()
def reverse(s):
    return s[::-1]
  Parameters 
name (Optional[str]) – the optional name of the filter, otherwise the function name will be used.  Return type 
Callable   
  
template_folder  
The path to the templates folder, relative to root_path, to add to the template loader. None if templates should not be added. 
  
template_global(name=None)  
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
  Changelog New in version 0.10.   Parameters 
name (Optional[str]) – the optional name of the global function, otherwise the function name will be used.  Return type 
Callable   
  
template_test(name=None)  
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
  Changelog New in version 0.10.   Parameters 
name (Optional[str]) – the optional name of the test, otherwise the function name will be used.  Return type 
Callable   
  
property templates_auto_reload: bool  
Reload templates when they are changed. Used by create_jinja_environment(). This attribute can be configured with TEMPLATES_AUTO_RELOAD. If not set, it will be enabled in debug mode.  Changelog New in version 1.0: This property was added but the underlying config and behavior already existed.  

  
test_cli_runner(**kwargs)  
Create a CLI runner for testing CLI commands. See Testing CLI Commands. Returns an instance of test_cli_runner_class, by default FlaskCliRunner. The Flask app object is passed as the first argument.  Changelog New in version 1.0.   Parameters 
kwargs (Any) –   Return type 
FlaskCliRunner   
  
test_cli_runner_class: Optional[Type[FlaskCliRunner]] = None  
The CliRunner subclass, by default FlaskCliRunner that is used by test_cli_runner(). Its __init__ method should take a Flask app object as the first argument.  Changelog New in version 1.0.  

  
test_client(use_cookies=True, **kwargs)  
Creates a test client for this application. For information about unit testing head over to 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, *args, **kwargs):
        self._authentication = kwargs.pop("authentication")
        super(CustomClient,self).__init__( *args, **kwargs)

app.test_client_class = CustomClient
client = app.test_client(authentication='Basic ....')
 See FlaskClient for more information.  Changelog Changed in version 0.11: Added **kwargs to support passing additional keyword arguments to the constructor of test_client_class.   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 0.4: added support for with block usage for the client.   Parameters 
 
use_cookies (bool) –  
kwargs (Any) –    Return type 
FlaskClient   
  
test_client_class: Optional[Type[FlaskClient]] = None  
the test client that is used with when test_client is used.  Changelog New in version 0.7.  

  
test_request_context(*args, **kwargs)  
Create a RequestContext for a WSGI environment created from the given values. This is mostly useful during testing, where you may want to run a function that uses request data without dispatching a full request. See The Request Context. Use a with block to push the context, which will make request point at the request for the created environment. with test_request_context(...):
    generate_report()
 When using the shell, it may be easier to push and pop the context manually to avoid indentation. ctx = app.test_request_context(...)
ctx.push()
...
ctx.pop()
 Takes the same arguments as Werkzeug’s EnvironBuilder, with some defaults from the application. See the linked Werkzeug docs for most of the available arguments. Flask-specific behavior is listed here.  Parameters 
 
path – URL path being requested. 
base_url – Base URL where the app is being served, which path is relative to. If not given, built from PREFERRED_URL_SCHEME, subdomain, SERVER_NAME, and APPLICATION_ROOT. 
subdomain – Subdomain name to append to SERVER_NAME. 
url_scheme – Scheme to use instead of PREFERRED_URL_SCHEME. 
data – The request body, either as a string or a dict of form keys and values. 
json – If given, this is serialized as JSON and passed as data. Also defaults content_type to application/json. 
args (Any) – other positional arguments passed to EnvironBuilder. 
kwargs (Any) – other keyword arguments passed to EnvironBuilder.   Return type 
flask.ctx.RequestContext   
  
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 test 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)  
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.  Changelog Changed in version 1.0: Bad request errors are not trapped by default in debug mode.   New in version 0.8.   Parameters 
e (Exception) –   Return type 
bool   
  
update_template_context(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 overridden if a context processor decides to return a value with the same key.  Parameters 
context (dict) – the context as a dictionary that is updated in place to add extra variables.  Return type 
None   
  
url_build_error_handlers: t.List[t.Callable[[Exception, str, dict], str]]  
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.  Changelog New in version 0.9.  

  
url_default_functions: t.Dict[AppOrBlueprintKey, t.List[URLDefaultCallable]]  
A data structure of functions to call to modify the keyword arguments when generating URLs, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests. To register a function, use the url_defaults() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
url_defaults(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.  Parameters 
f (Callable[[str, dict], None]) –   Return type 
Callable[[str, dict], None]   
  
url_map  
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(super(ListConverter, self).to_url(value)
                        for value in values)

app = Flask(__name__)
app.url_map.converters['list'] = ListConverter
 
  
url_map_class  
alias of werkzeug.routing.Map 
  
url_rule_class  
alias of werkzeug.routing.Rule 
  
url_value_preprocessor(f)  
Register a URL value preprocessor function for all view functions in the application. These functions will be called before the before_request() functions. The function can modify the values captured from the matched url before they are passed to the view. For example, this can be used to pop a common language code value and place it in g rather than pass it to every view. The function is passed the endpoint name and values dict. The return value is ignored.  Parameters 
f (Callable[[Optional[str], Optional[dict]], None]) –   Return type 
Callable[[Optional[str], Optional[dict]], None]   
  
url_value_preprocessors: t.Dict[AppOrBlueprintKey, t.List[URLValuePreprocessorCallable]]  
A data structure of functions to call to modify the keyword arguments passed to the view function, in the format {scope: [functions]}. The scope key is the name of a blueprint the functions are active for, or None for all requests. To register a function, use the url_value_preprocessor() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
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.  Changelog 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: t.Dict[str, t.Callable]  
A dictionary mapping endpoint names to view functions. To register a view function, use the route() decorator. This data structure is internal. It should not be modified directly and its format may change at any time. 
  
wsgi_app(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 app object. 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.  Changelog Changed in version 0.7: Teardown events for the request and app contexts are called even if an unhandled error occurs. Other events may not be called depending on when an error occurs during dispatch. See Callbacks and Errors.   Parameters 
 
environ (dict) – A WSGI environment. 
start_response (Callable) – A callable accepting a status code, a list of headers, and an optional exception context to start the response.   Return type 
Any