Develop Reference

How do I create a web application using Core Python without a framework?

I want to build an web application using python as a backend so, as I did not learned any of the web frameworks that are available for python I want to know is there any way to create backend for an app without frameworks.

While there is a discussion in the comments about the utility of frameworks, I am trying to answer the question at its face value.
WSGI
Python frameworks like Flask and Django both at the end are WSGI applications. WSGI (Web Service Gateway Interface) is a PEP specification which defines how the server and client must communicate. If I were to start from scratch, I would probably start with learning about WSGI and even try implementing a little ping-pong server with it. The read the docs page here https://wsgi.readthedocs.io/en/latest/learn.html lists a number of pages to learn about it.
Werkzeug
Once the WSGI specs are understood then one can attempt building a simple library that will wrap the core concepts into reusable functions and modules for easily writing an application. Here Werkzeug can be a good guide to make one understand the different aspects. https://www.palletsprojects.com/p/werkzeug/
Your own application
Based on the understanding of the WSGI spec and the Werkzueg library you can go on to write your applications either from scratch, or write a library like werkzueg yourself and then use it to write an application.
Finally reimplement the same app in Flask or Django to see what frameworks offer.

If it's something small for internal use you can use
https://docs.python.org/3/library/http.server.html

Python or Node.js for a Web app which interfaces with a USB devices?

I'm looking to develop a web app that controls Concept2 rowing gym equipment connected to the users computer via USB. I'm trying to decide what approach I should take in developing something like this.
Control of these devices has been achieved in the past both in python:
(https://github.com/uvd/PyRow)
and using node/jQuery:
(https://github.com/tijmenvangulik/ErgometerJS).
An SDK and documentation is provided by the developers of Concept2 gym equipment. DLL and CSafe commands are used to interface with the machines monitors.
(https://www.concept2.com/service/software/software-development-kit)
I'm looking for recommendations on how I should this tackle this project. At the moment python seems like the best approach however I have no idea how I can run these python files through a website interacting with the java script front end.
Any advice or pointers is appreciated.
David

You task looks like a simple SCADA solution with web interface.
You choice depends on whether you have experienced developers, who are able to use modern frameworks like Vue.js, Angular, React and others or not.
Really, in your particular case - monitoring equipment over web, you don't necessary need to invest a lot in your front-end - depends on your target audience. Is it a single service engineer? If yes, probably your front-end should be minimalistic, you can use Python with Twisted for static web server and build your frontend on bootstrap plus jquery. This is a fast win solution and you can implement it even if you've never worked with web.
More complex approach, requiring more engineering, is Python + Flask.
If you feel ready for modern frameworks, like Vue, React, Angular, then, possibly, you'd better look at NodeJs as a backend. They are better integrated with NodeJs and its package manager npm. You will need it to build the project on your server side; also some people treat it as a solid solution, when using the same language (javascript) for both backend and frontend. As for me, it doesn't really matter a lot.

Amazon AWS - Python webframework - dynamodb

I've done a lot of research for Google App engine. I ended up with webapp2. Now we realized that AWS has many advantages over GAE for our project.
I feel a little bit overwhelmed because there is so much information about AWS.
I ended up with the nosql dynamoDB solution.
Now I really love lightweight frameworks like webapp2 , its really simple and easy to use. It also don't hide post and get from you.
Now does it makes sense to use webapp2 for AWS ? Mabye there other frameworks that would fit better for our project.
(We want to go in a filehosting direction)
I mean there are literally 50 frameworks for python. And I didn't find a chart with pro/cons.
The last frameworks that I investigated are : web2py , pylon(now pyramids?) and tornado.
To be honest I am really confused.
So if I want to have a lightweight framework for AWS would you recommend me to stay with webapp2?
Resources:
Amazon AWS web framework for Python
Edit #1
Now it's a decision between tornado and webapp2. considering that I want to use dynamoDB.

Tornado is a fast non-blocking web server itself. It's easy to write simple apps in a few minutes, but it has nothing AFAIK like templates, views, etcetera. If you want to serve files it would be very quick to connect a tornado server together with boto (https://github.com/boto/boto) and use dynamoDB or S3.
On the other hand, pylons (now pyrmaid) and we2py are full web application frameworks with no web server. In fact, they come with a lightweight development server (at least pylons), but if you want to put up a site in AWS you should use something like nginx (http://nginx.org/), apache or some other wsgi server (http://wsgi.readthedocs.org/).
If you want to go for a lightweight framework and use python, I'd go for web2py, easy to configure and build apps. (A curious note: it used to be a single .py file) you can try it online: http://www.web2py.com/demo_admin/default/site
Regarding webapp2 I've never used it, but I've heard it's similar to Appengine web framework. So if you're comfortable with it stay there.
Either direction, boto is the python interface for AWS so if you choose python, you'll have to check it out. It is actively mantained.

What python based ajax push servers are good to work with

I have a web application im currently working on in python. I'm using Django as my web framework currently. I intend to integrate real-time web features into the application using ajax push. However, I'm a bit confused as to what python based push server i should adopt. I've heard of a few of them, Orbited, Gevent, Tornado, but my main issue right now is that i'm a green horn when it comes to realtime web applications. I'd like to use python and i'd like a framework with good documentation.

A lot of people choose gevent for webapps with real-time features because of the speed, ease of use and a number of supporting packages.
Take a look at these packages:
gevent-socketio
django-socketio
and these tutorials:
Evented Django part one: Socket.IO and gevent
New and hot, part 4: Pyramid, Socket.IO and Gevent
Real-time Web Apps with Django and WebSockets
Hope this helps.

APE seems a cool thing.
I think it's not a problem to make it work with PDjango as a backend.

I think the most popular is tornado open-sourced by facebook. It also has pretty decent documentation.

What is the simplest way to offer/consume web services in jython?

I have an application for Tomcat which needs to offer/consume web services. Since Java web services are a nightmare (xml, code generation, etc.) compared with what is possible in Python, I would like to learn from your experience using jython instead of java for offerring/consuming web services.
What I have done so far involves adapting http://pywebsvcs.sourceforge.net/ to Jython. I still get errors (namespaces, types and so), although some of it is succesful for the simplest services.

I've put together more details on how to use webservices in jython using axis. Read about it here: How To Script Webservices with Jython and Axis.

PyServlet helps you configure Tomcat to serve up Jython scripts from a URL. You could use this is a "REST-like" way to do some basic web services without much effort. (It is also described here.)
We used a similar home grown framework to provide a variety of data services in a large multiple web application very successfully.