I used requests to login to a website using the correct credentials initially. Then I tried the same with some invalid username and password. I was still getting response status of 200. I then understood that the response status tells if the corresponding webpage has been hit or not. So now my doubt is how to verify if I have really logged in to the website using correct credentials
What status code the site responds with depends entirely on their implementation; you're more likely to get a non-200 response if you're attempting to log in to a web service. If a login attempt yielded a non-200 response on a normal website, it'd require a special handler on their end, as opposed to a 200 response with a normal page prompting you (presumably a human user, not a script) with a visual cue indicating login failure.
If the site you're logging into returns a 200 regardless of success or failure, you may need to use something like lxml or BeautifulSoup to look for indications of success or failure (which presumably you'll be using already to process whatever it is you're logging in to access).
How to verify that we have logged in correctly to a website using requests in python?