The Web Server Gateway Interface defines a simple and universal interface between web servers and web applications or frameworks for the Python programming language.
Idea
Python boasts a wide variety of web application frameworks. This can be a problem for new Python users because, generally speaking, their choice of web framework will limit their choice of usable web servers, and vice versa.
WSGI proposes a simple and universal interface between web servers and web applications or frameworks.
Specification overview
The WSGI interface has two sides: the "server" or "gateway" side, and the "application" or "framework" side. The server side invokes a callable object (usually a function or a method) that is provided by the application side. Additionally WSGI provides middlewares, components that play both sides.
A "middleware" component can perform such functions as:
- Routing a request to different application objects based on the target URL, after changing the environment variables accordingly.
- Allowing multiple applications or frameworks to run side-by-side in the same process
- Load balancing and remote processing, by forwarding requests and responses over a network
- Perform content postprocessing, such as applying XSL stylesheets
Example application
A WSGI compatible "Hello World" application:
def app(environ, start_response):
start_response('200 OK', [('Content-Type', 'text/plain')])
return ['Hello World\n']
WSGI-compatible applications and frameworks
There are numerous Web application frameworks supporting WSGI:
Additionally there are two simple publishers:
Wrappers
The server or gateway invokes the application callable once for each request it receives from an HTTP client, that is directed at the application.
Currently wrappers are available for FastCGI, CGI, SCGI, AJP using the flup package.
External links
- PEP 333 defining the interface standard
- http://www.pythonpaste.org/ - WSGI metaframework
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