python GUI - which to use ?

[snippsat]

A was more talking about Qt Designer when i said free to use and install.
For all Qt product if release as a commercial product need a Riverbank Commercial License(550$ a year).
There a two branches PyQt5 and PySide2(also now known as Qt for Python).
The both need the Riverbank license,but Pyside2(Qt for Python) has a LGPL licence,allows you to distribute closed-source application.
With PyQt5 under GNU GPL v3,means you will need to publish the source code of your application.

If you are developing open-source software,it doesn't matter which one to use.
If thinking of distribute closed-source then need to go for Qt for Python.

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What is the difference between:
pip install PyQt5 and
Pip install PyQt5-tools

PyQt5-tools has the Qt Designer and some other tool like converting .ui(files) and more.

They all install the design software
to help design the GUI ?

No only Qt Designer has GUI to help with design.
I do not use a Designer when writing GUI,also write code test look/functionally,then repeat.

I do this installation following your
steps by going to command line and which folder ?

What if there is proxy blockage ?

The all go to site-packages or Scripts folder(binary executable).
You need to look more into pip(package manager for Python).
Behind a proxy,pip has tool for this,or can copy over a wheel.

# Use proxy
pip install --proxy=https://user@mydomain:port pyqt5

# Use wheel
pip install PyQt5-5.13.0-5.13.0-cp35.cp36.cp37.cp38-none-win_amd64.whl

If use Windows can look at link under,see that i show how pip shall work.
Python 3.6/3.7 and pip installation under Windows