Useful Functions and Classes ​

flask.current_app ​

A proxy to the application handling the current request. This is useful to access the application without needing to import it, or if it can’t be imported, such as when using the application factory pattern or in blueprints and extensions.

This is only available when an application context is pushed. This happens automatically during requests and CLI commands. It can be controlled manually with app_context().

This is a proxy. See Notes On Proxies for more information.

flask.has_request_context() ​

If you have code that wants to test if a request context is there or not this function can be used. For instance, you may want to take advantage of request information if the request object is available, but fail silently if it is unavailable.

class User(db.Model):

    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and has_request_context():
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

class User(db.Model):

    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and has_request_context():
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

Alternatively you can also just test any of the context bound objects (such as request or g) for truthness:

class User(db.Model):

    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and request:
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

class User(db.Model):

    def __init__(self, username, remote_addr=None):
        self.username = username
        if remote_addr is None and request:
            remote_addr = request.remote_addr
        self.remote_addr = remote_addr

Return type: bool

flask.copy_current_request_context(f) ​

A helper function that decorates a function to retain the current request context. This is useful when working with greenlets. The moment the function is decorated a copy of the request context is created and then pushed when the function is called. The current session is also included in the copied request context.

Example:

import gevent
from flask import copy_current_request_context

@app.route('/')
def index():
    @copy_current_request_context
    def do_some_work():
        # do some work here, it can access flask.request or
        # flask.session like you would otherwise in the view function.
        ...
    gevent.spawn(do_some_work)
    return 'Regular response'

import gevent
from flask import copy_current_request_context

@app.route('/')
def index():
    @copy_current_request_context
    def do_some_work():
        # do some work here, it can access flask.request or
        # flask.session like you would otherwise in the view function.
        ...
    gevent.spawn(do_some_work)
    return 'Regular response'

Parameters:

• f (Callable) –

Return type: Callable

flask.has_app_context() ​

Works like has_request_context() but for the application context. You can also just do a boolean check on the current_app object instead.

Return type: bool

flask.url_for(endpoint, *, _anchor=None, _method=None, _scheme=None, _external=None, **values) ​

Generate a URL to the given endpoint with the given values.

This requires an active request or application context, and calls current_app.url_for(). See that method for full documentation.

Parameters:

• endpoint (str) – The endpoint name associated with the URL to generate. If this starts with a ., the current blueprint name (if any) will be used.

• _anchor (str | None) – If given, append this as #anchor to the URL.

• _method (str | None) – If given, generate the URL associated with this method for the endpoint.

• _scheme (str | None) – If given, the URL will have this scheme if it is external.

• _external (bool | None) – If given, prefer the URL to be internal (False) or require it to be external (True). External URLs include the scheme and domain. When not in an active request, URLs are external by default.

• values (Any) – Values to use for the variable parts of the URL rule. Unknown keys are appended as query string arguments, like ?a=b&c=d.

Return type: str

flask.abort(code, *args, **kwargs) ​

Raise an HTTPException for the given status code.

If current_app is available, it will call its aborter object, otherwise it will use werkzeug.exceptions.abort().

Parameters:

• code (int | BaseResponse) – The status code for the exception, which must be registered in app.aborter.

• args (t.Any) – Passed to the exception.

• kwargs (t.Any) – Passed to the exception.

Return type: t.NoReturn

flask.redirect(location, code=302, Response=None) ​

Create a redirect response object.

If · is available, it will use its redirect() method, otherwise it will use werkzeug.utils.redirect().

Parameters:

location (str) – The URL to redirect to.

code (int) – The status code for the redirect.

Response (type[BaseResponse] | None) – The response class to use. Not used when current_app is active, which uses app.response_class.

Return type: BaseResponse

flask.make_response(*args) ​

Sometimes it is necessary to set additional headers in a view. Because views do not have to return response objects but can return a value that is converted into a response object by Flask itself, it becomes tricky to add headers to it. This function can be called instead of using a return and you will get a response object which you can use to attach headers.

If view looked like this and you want to add a new header:

def index():
    return render_template('index.html', foo=42)

def index():
    return render_template('index.html', foo=42)

You can now do something like this:

def index():
    response = make_response(render_template('index.html', foo=42))
    response.headers['X-Parachutes'] = 'parachutes are cool'
    return response

def index():
    response = make_response(render_template('index.html', foo=42))
    response.headers['X-Parachutes'] = 'parachutes are cool'
    return response

This function accepts the very same arguments you can return from a view function. This for example creates a response with a 404 error code:

response = make_response(render_template('not_found.html'), 404)

response = make_response(render_template('not_found.html'), 404)

The other use case of this function is to force the return value of a view function into a response which is helpful with view decorators:

response = make_response(view_function())
response.headers['X-Parachutes'] = 'parachutes are cool'

response = make_response(view_function())
response.headers['X-Parachutes'] = 'parachutes are cool'

Internally this function does the following things:

• if no arguments are passed, it creates a new response argument

• if one argument is passed, flask.Flask.make_response() is invoked with it.

• if more than one argument is passed, the arguments are passed to the flask.Flask.make_response() function as tuple.

Parameters:

• args (t.Any) –

Return type: Response

flask.after_this_request(f) ​

Executes a function after this request. This is useful to modify response objects. The function is passed the response object and has to return the same or a new one.

Example:

@app.route('/')
def index():
    @after_this_request
    def add_header(response):
        response.headers['X-Foo'] = 'Parachute'
        return response
    return 'Hello World!'

@app.route('/')
def index():
    @after_this_request
    def add_header(response):
        response.headers['X-Foo'] = 'Parachute'
        return response
    return 'Hello World!'

This is more useful if a function other than the view function wants to modify a response. For instance think of a decorator that wants to add some headers without converting the return value into a response object.

Parameters:

• f (Callable[[ResponseClass], ResponseClass] | Callable[[ResponseClass], Awaitable[ResponseClass]]) –

Return type: Callable[[ResponseClass], ResponseClass] | Callable[[ResponseClass], Awaitable[ResponseClass]]

flask.send_file(path_or_file, mimetype=None, as_attachment=False, download_name=None, conditional=True, etag=True, last_modified=None, max_age=None) ​

Send the contents of a file to the client.

The first argument can be a file path or a file-like object. Paths are preferred in most cases because Werkzeug can manage the file and get extra information from the path. Passing a file-like object requires that the file is opened in binary mode, and is mostly useful when building a file in memory with io.BytesIO.

Never pass file paths provided by a user. The path is assumed to be trusted, so a user could craft a path to access a file you didn’t intend. Use send_from_directory() to safely serve user-requested paths from within a directory.

If the WSGI server sets a file_wrapper in environ, it is used, otherwise Werkzeug’s built-in wrapper is used. Alternatively, if the HTTP server supports X-Sendfile, configuring Flask with USE_X_SENDFILE = True will tell the server to send the given path, which is much more efficient than reading it in Python.

Parameters:

• path_or_file (os.PathLike | str | t.BinaryIO) – The path to the file to send, relative to the current working directory if a relative path is given. Alternatively, a file-like object opened in binary mode. Make sure the file pointer is seeked to the start of the data.

• mimetype (str | None) – The MIME type to send for the file. If not provided, it will try to detect it from the file name.

• as_attachment (bool) – Indicate to a browser that it should offer to save the file instead of displaying it.

• download_name (str | None) – The default name browsers will use when saving the file. Defaults to the passed file name.

• conditional (bool) – Enable conditional and range responses based on request headers. Requires passing a file path and environ.

• etag (bool | str) – Calculate an ETag for the file, which requires passing a file path. Can also be a string to use instead.

• last_modified (datetime | int | float | None) – The last modified time to send for the file, in seconds. If not provided, it will try to detect it from the file path.

• max_age (None | (int | t.Callable[[str | None], int | None])) – How long the client should cache the file, in seconds. If set, Cache-Control will be public, otherwise it will be no-cache to prefer conditional caching.

Return type: Response

flask.send_from_directory(directory, path, **kwargs) ​

Send a file from within a directory using send_file().

@app.route("/uploads/<path:name>")
def download_file(name):
    return send_from_directory(
        app.config['UPLOAD_FOLDER'], name, as_attachment=True
    )

@app.route("/uploads/<path:name>")
def download_file(name):
    return send_from_directory(
        app.config['UPLOAD_FOLDER'], name, as_attachment=True
    )

This is a secure way to serve files from a folder, such as static files or uploads. Uses safe_join() to ensure the path coming from the client is not maliciously crafted to point outside the specified directory.

If the final path does not point to an existing regular file, raises a 404 NotFound error.

Parameters:

• directory (os.PathLike | str) – The directory that path must be located under, relative to the current application’s root path.

• path (os.PathLike | str) – The path to the file to send, relative to directory.

• kwargs (t.Any) – Arguments to pass to send_file().

Return type: Response