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WSGI interface
The WSGI interface definition is very simple, it only requires web developers to implement a function to respond to HTTP requests. Let's look at the simplest web version of "Hello, web!":
def application(environ, start_response):
start_response('200 OK', [('Content-Type', 'text/html')])
return '<h1>Hello, web!</h1>'
The above application()function is an HTTP processing function that conforms to the WSGI standard, and it receives two parameters:
environ: a dict object containing all HTTP request information;start_response: A function that sends an HTTP response.
In application()the function, call:
start_response('200 OK', [('Content-Type', 'text/html')])
The Header of the HTTP response is sent. Note that the Header can only be sent once, that is, start_response()the function can only be called once. start_response()The function receives two parameters, one is the HTTP response code, and the other is a set of HTTP Headers represented by a list, and each Header is represented by a tuple containing two strs.
Normally, Content-Typethe header should be sent to the browser. Many other commonly used HTTP headers should also be sent.
Then, the return value of the function '<h1>Hello, web!</h1>'will be sent to the browser as the Body of the HTTP response.
With WSGI, what we care about is how to environget the HTTP request information from this dict object, then construct HTML, start_response()send the Header, and finally return the Body.
The whole application()function itself does not involve any part of parsing HTTP, that is to say, the underlying code does not need to be written by ourselves, we are only responsible for considering how to respond to requests at a higher level.
But wait, application()how is this function called? If we call it ourselves, we cannot provide the sum of the two parameters , environand start_responsethe returned str cannot be sent to the browser.
So application()the function must be called by the WSGI server. There are many servers that conform to the WSGI specification, and we can choose one to use. But now, we just want to test as soon as possible that the function we wrote application()can really output HTML to the browser, so we must quickly find the simplest WSGI server and run our web application.
The good news is that Python has a built-in WSGI server, this module is called wsgiref, and it is the reference implementation of a WSGI server written in pure Python. The so-called "reference implementation" means that the implementation fully complies with the WSGI standard, but does not consider any operational efficiency, and is only used for development and testing.
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