What is CGI in Python ?

CGI stands for Common Gateway Interface in Python which is a set of standards that explains how information or data is exchanged between the web server and a routine script. This interface is used by web servers to route information requests supplied by a browser or we can say that CGI is customary for external gateway programs to interface with information servers such as HTTP servers. 
A CGI script is invoked by an HTTP server, usually to course user input which is submitted through an HTML <FORM> or an <ISINDEX> element.

Concept of CGI 

Whenever we click on a hyperlink to browse a particular web page or URL, our browser interacts with the HTTP web server and asks for the same URL (or filename). Web Server then parses the URL and looks for the same filename. If that file is found, then that file is sent back to the browser, otherwise, an error message is sent indicating that we are demanding a wrong file. Web browser takes the response from a web server and displays it, then whether it is the received file from the webserver or an error message. But, conversely, it is possible to set up the HTTP server so that whenever a specific file is requested, then that file is not sent back, but instead, it is executed as a program, and whatever that program output is, that is sent back to our browser for display. This same function is called the Common Gateway Interface (or CGI) and the programs which are executed are called CGI scripts. In python, these CGI programs is a Python Script.

Architecture of CGI:
 

Example:
Let us take a sample URL which passes two values to first_cgi.py program using GET method:
/cgi-bin/first_cgi.py?your_name=Piyush&company_name=GeeksforGeeks

Below is the first_cgi.py script to handle the input given by the above sample URL. Here we will use cgi module which will makes it very easy to access the passed information 
 

Python3

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#!/usr/bin/python
  
# Import CGI and CGIT module
import cgi, cgitb              
  
# to create instance of FieldStorage 
# class which we can use to work 
# with the submitted form data
form = cgi.FieldStorage()      
your_name = form.getvalue('your_name')    
  
# to get the data from fields
comapny_name = form.getvalue('company_name')   
  
print ("Content-type:text/html\n")
print ("<html>")
print ("<head>")
print ("<title>First CGI Program</title>")
print ("</head>")
print ("<body>")
print ("<h2>Hello, %s is working in %s</h2>" 
       % (your_name, company_name))
  
print ("</body>")
print ("</html>")

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Output:

 Hello, Piyush is working in GeeksforGeeks 
My Personal Notes arrow_drop_up

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