API

This part of the documentation covers all the interfaces of Flask. For parts where Flask depends on external libraries, we document the most important right here and provide links to the canonical documentation.

Application Object

Incoming Request Data

class request

To access incoming request data, you can use the global request object. Flask parses incoming request data for you and gives you access to it through that global object. Internally Flask makes sure that you always get the correct data for the active thread if you are in a multithreaded environment.

The request object is an instance of a Request subclass and provides all of the attributes Werkzeug defines. This just shows a quick overview of the most important ones.

form

A MultiDict with the parsed form data from POST or PUT requests. Please keep in mind that file uploads will not end up here, but instead in the files attribute.

args

A MultiDict with the parsed contents of the query string. (The part in the URL after the question mark).

values

A CombinedMultiDict with the contents of both form and args.

cookies

A dict with the contents of all cookies transmitted with the request.

stream

If the incoming form data was not encoded with a known encoding (for example it was transmitted as JSON) the data is stored unmodified in this stream for consumption. For example to read the incoming request data as JSON, one can do the following:

json_body = simplejson.load(request.stream)

files

A MultiDict with files uploaded as part of a POST or PUT request. Each file is stored as FileStorage object. It basically behaves like a standard file object you know from Python, with the difference that it also has a save() function that can store the file on the filesystem.

environ

The underlying WSGI environment.

method

The current request method (POST, GET etc.)

path

script_root

url

base_url

url_root

Provides different ways to look at the current URL. Imagine your application is listening on the following URL:

http://www.example.com/myapplication

And a user requests the following URL:

http://www.example.com/myapplication/page.html?x=y

In this case the values of the above mentioned attributes would be the following:

path	/page.html
script_root	/myapplication
url	http://www.example.com/myapplication/page.html
base_url	http://www.example.com/myapplication/page.html?x=y
root_url	http://www.example.com/myapplication/

Response Objects

Sessions

If you have the Flask.secret_key set you can use sessions in Flask applications. A session basically makes it possible to remember information from one request to another. The way Flask does this is by using a signed cookie. So the user can look at the session contents, but not modify it unless he knows the secret key, so make sure to set that to something complex and unguessable.

To access the current session you can use the session object:

class session

The session object works pretty much like an ordinary dict, with the difference that it keeps track on modifications.

The following attributes are interesting:

new

True if the session is new, False otherwise.

modified

True if the session object detected a modification. Be advised that modifications on mutable structures are not picked up automatically, in that situation you have to explicitly set the attribute to True yourself. Here an example:

# this change is not picked up because a mutable object (here
# a list) is changed.
session['objects'].append(42)
# so mark it as modified yourself
session.modified = True

Application Globals

To share data that is valid for one request only from one function to another, a global variable is not good enough because it would break in threaded environments. Flask provides you with a special object that ensures it is only valid for the active request and that will return different values for each request. In a nutshell: it does the right thing, like it does for request and session.

g

Just store on this whatever you want. For example a database connection or the user that is currently logged in.

Useful Functions and Classes

abort(code)

Raises an HTTPException for the given status code. For example to abort request handling with a page not found exception, you would call abort(404).

参数:

code -- the HTTP error code.

Message Flashing

Template Rendering