SO is not a tutorial. The format does not lend itself well to teaching a new language starting from basics. Yes, taken together the questions illuminate a lot of a given language, but there will be dark spots which not only aren't described here, there aren't any clues that tell you your missing something.
That last point is important - without a 'language roadmap' of some sort, you won't learn some basic aspects of the language, you won't know that you're missing parts of it, and that will hobble you in the future.
So no, you cannot expect to fully learn a language on SO with no outside resources.
SO is a great place to enhance a good tutorial, though. If you are already an accomplished programmer, you may be able to dig into the meat of the language, and while going through basic instruction look up related questions on SO to drill down into why or when one might choose one construct over another. You might use SO to teach you advanced topics that are glossed over in the basic tutorial, since it's geared towards someone who may not understand advanced CS topics.
But I'd be interested in seeing someone try. I suspect that SO could become a good resource if someone took the time to put together a series of questions that became the tutorial:
"This is part of a series on learning Python for beginners. Please read the question carefully, and submit answers that are simple, clear and easy to understand. Your answer should answer the question with as much detail as necessary for a beginner - but no more. Please do not post an answer consisting only of links - the intent is to build a fully self-supporting tutorial for Python on SO."
The above would appear at the top of every tutorial question, and you might have the following basic questions (each in its own question post):
- What is the history of Python - who created, why, and what are its roots (in terms of other languages that preceded it)? What languages have claimed this language as one of their influences?
- What are the basic constructs of Python?
- What are the control structures of Python?
- What are variables in Python, and how are they used?
You'll probably need to CW the post to avoid the wiki police, but other than that there's no reason not to post a tutorial series of questions, and thereby learn a language while providing a resource for others who might want to learn a given language.
Expect, though, that once someone starts doing this, these will pop up all over the place as others will follow suit. It may result in a backlash from the community (all I see are these stupid tutorials!) but I believe this could be a very good resource for programmers, and a way to bring beginners into the community on a regular basis.