How to display the webdriver window only in one specific condition using selenium (python)?
No, its not possible.
Only way is to use several browsers.
As example:

run phantomJS(headless browser)
run do needed actions
run firefox, used perform login
copy cookies after login
paste cookies to phantomJS
close firefox
How do I only display the screen of my webdriver in a specific case using selenium? 
I only want to display the window to the user when the title of the page is for exemple "XXX", so then he type something one the window and than the window close again, and the robot continue making what he should make on background.
Is it possible?
Thanks,