allow instantiating corrections with different constructors

[mroguljic]

No description provided.

[lcorcodilos]

@mroguljic I'm finally getting the chance to look at this. Can you explain briefly the intention of isNewConstr and put a description in the docstring with a new @param line?

My only other question is about the changes to setup.py to change to >=. There are some issues doing this with python 2.7. As you can see from the failing GitHub tests, it's trying to use a version of pandas using f string formatting that doesn't work in python 2.7.

Of course, if CMS has finally released a CMSSW version with python 3+ROOT that works and is now standard, we can ignore that :-)

[mroguljic]

@lcorcodilos
isNewConstr was placed so I can instantiate a Correction object which uses the same main function as some already created Correction, but with different arguments provided to the constructor which usually initializes the file/histogram needed for correction. Example of the usage can be found here: https://github.com/mroguljic/Zbb_SF/blob/v1/templateMaker.py#L165-L166

As far as I'm aware, the isClone flag does not provide this option. If this makes sense, I'll go ahead and document this as you proposed.

Regarding the setup.py. I was not aware this was bundled in the PR and it shouldn't be here. This was me trying to test python3 installation. Indeed, there is now a setup which works with CMSSW_12_X and python3. I'll make a separate PR for this once we resolve the first item.