I want to establish one session at the starting of the suite. That session should be stay for longer time for multiple test cases.That session should end at the last.
That session should be implement in Selenium Web driver by using Unittest frame works in python language.
please can anyone suggest any methods or how to implement it.
The simplest way to achieve this is not to use the Setup() and TearDown() methods, or more specifically not to create a new instance of the WebDriver object at that start or each test case, and not to use the Quit() method at the end of each test case. 
In your first test case create a new instance of the WebDriver object and use this object for all of your test cases. At the end of your last test case use the Quit() method to close the browser.
how to establish a session thourghout the selenium webdriver suite by using python in firefox