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ReactJS with Python as Backend

What is the best approach to use ReactJS as front end and Python as a backend? I already built a tool using Tkinter which have simple UI. I want to use ReactJS and rebuild this application that anyone can install on their desktops. Is it possible? If so can anyone briefly explain the workflow or any online resources would be appreciated. Thank you! (I have a basic knowledge using Djnago)

Its a great idea in the modern world of web technology, using ReactJS as a frontend and Django Rest Framework to make your API, and Django for the backend aspect is a great choice as you could utilize the API in other application such as a mobile application.
I would suggest you go with those technologies as most big and medium scale websites now uses ReactJs with Django/Django Rest Framework or some other backend tools.
If you have any other question, i would be glad to answer it.
Thanks and have a great day.

Sure, people have used React for their desktop applications. Slack for example have used React in there desktop applications so you are in good company there ;)
https://slack.engineering/rebuilding-slack-on-the-desktop/
But why not just put your UI in a simple web application with React and avoid the hassle to support multiple operating systems and versions?

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

How to make a web app for simple python text processing

I have made a python program which does some text processing to whatever input I give and for now run I it simply by our terminal window(cmd). But now we want to make a simple web app which takes the input from user and then my application processes it and then the result is shown to user. Something like http://textanalysisonline.com/simple-text-summarizer.
As i am new to all this any help would be appreciated. thanks

I suggest looking into using Django - A framework for making python (web) applications.
I would look into downloading the python IDE PyCharm as it makes Django development quite easy and then look into some tutorials on how to make Django applications.
then I would install Django and then follow the tutorials (maybe start here) for figuring out how to add your script to a Django application. Happy coding!

How to use python to do the web development (or how to set uo cgi)

As the title said, just wonderring how to use python or anyhow to include executable python script into HTML

Using django to do this.
django official web:
https://www.djangoproject.com/

I would look into the python documentation here for learning about Python in the web. But more specifically, there is documentation here explaining Common Gateway Interface (CGI) and how to use it. I recommend looking into this first because I am unsure what exactly you need help with, if it is simply wondering how it works, then these links will explain that just fine.

Flask is very simple micro framework for writing web applications in python.
http://flask.pocoo.org

REST web service in python 3?

I'm new to the python world and I'm currently in a new project using it. So since we we're there to learn, we chose to start with python 3. Now, we need to make a RESTful web service. After reading a few, I found out that the most used framework for web services is Django... and I also read on the Django website that it does not yet supports python 3.
Is there any other API that I could use in order to make a RESTful web service?
Thank you.

CherryPy has a Python 3 branch. Not sure how advanced it is, but if Fu-manchu passes by this question, he will be able to tell you.

The Bottle framework claims to work with Python 3. You might inquire on their google group for details.

I really like to use bottle and run it on cherrypy. This is really easy, do everything per bottle instructions, and then in the run line, tell it to use cherrypy as it's server.
Exampple:
app.run(host='localhost',
port=8080,
server='cherrypy',
reloader=True,
debug=True)