M K Sri Datta

Python is very easy to learn and implement, but it can be considered versatile.
main python applications are Machin learning, AI, Data analytics.
it can also be used for Web development- Django and flask are very famous python frameworks for backend development.
but when coming to game development, frontend development, and such there are many other languages that are better suited(like java and javascript).

nowadays there are many new applications are being developed like qlik and dash for visualization and son based on python.

python is well liked and and widely used (in specific domain/fields).

Not required.
python basics are mandatory for everything.
depending on your expecting job role and area of interest you can learn libraries.
but libraries like NumPy and pandas are a must and should in many cases.
if you are into machine learning go for scipy
for visualization matplotlib
for NLP python nltk library

and so on it is highly impossible for anyone to learn all the python libraries.
just go for whatever you feel necessary,you can always come back and learn missing things when ever it's required

First, start looking for a python video tutorial on youtube where every video is free and most of the python content is free.
suggested videos:

python for everybody - MOOC course 13hr content by Dr chuck severance

python tutorial for beginners - by programming with mosh

to practice online use IBM's skill network labs(search in google) for online Jupiter lab

for any doubts look at geeks for geeks website or w3 schools or stack overflow

to find practice questions or examples try HackerEarth or hackerrank