Python is an easier language to work with, across the board. Well-written C++ runs significantly faster than Python. Those are your 2 main concerns.

Neither is really 'better' at graphics, or logic, or procedural generation.

Pygame doesn't include a physics simulation system. There may be 3rd party ones available. Most of the physics engines are written in C or C++ and then they can often be used with Python as well. Box2D is one example.

The tooling side of Gamesalad is certainly something you could make in Python, but it would be a large undertaking to do so. But then it would be a large undertaking in C++ too. The features you need from your "builder" are even more important than the features you need in your game, when it comes to how complex this task would be.

It really depends on your goals.

I'll describe which goals you'll achieve with each:

C++
- Good 3D graphics.

- Usage of low level api (More control- Harder to master/learn)

- Building big games.

- Be in the industry standards.

- You have time.

Python:

- Good for 2D.

- Fast development.

- Low on budget. (In case you want to sell the game).

Other goals that are not mentinoed here are pretty much equal.

The Biggest deference is speed.. You can have a prototype of your game written in python in an afternoon. C++ executes faster. python has a super extensive third party library collection which means most of the grunt work is already done. Also. pretty much all platforms have a python interpreter available, meaning, as long as you follow pythons conventions(using the Path class, etc) your program would run on win32, linux, and mac.

HOWEVER. python has a very long( comparatively speaking) execution time. if your game is even a little graphically intense, you will have a lot of frame rate issues. C++ on the other hand is super fast check out a project called irrlicht, it is a supper easy to use graphics engine, that is lightweight and fast. To answer your question directly about the side scroller, if its is 3D and you plan to add a lot of effects to make it look cool, stick with c++. but if is going to be really simple ( or simple 3D) python will have you up and running way faster. That may be very important if you are working by yourself.

help with panda3D(popular python graphics engine)https://www.panda3d.org/manual/index.php/Performance_Tuning

irrlicht project: