Allowing material making from class constructor

[shimwell]

Description

It have just added a minimal set of extra options to the Material constructor to allow a material to made from the constructor.

This is useful to myself as I have a json representation of the material and going to a material object is easier with this addition. It also follows on some work @eepeterson and myself were doing trying to allow more classes to be construct-able from the constructor.

Fixes # (issue)

Checklist

• I have performed a self-review of my own code
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[shimwell]

edited this PR
I had originally added nuclides to the constructor but have now removed that as there are a few ways go about the addition of elements/nuclides and I would now like to do that in a follow up PR to keep this one as minimal as possible. I think this makes it easier to consider for merging.

[paulromano]

Having objects be in a fully valid state after calling __init__ is a good idea 👍 So, I'm supportive of the change here, but wondering if there was a reason that you didn't also add a components argument that gets passed to add_components while you were at it? That would make it truly complete.

[paulromano]

How do you feel about having density_units default to "g/cm3"? In that case, the first branch of the if could just be removed.

[shimwell]

I would be happy with that density of 'g/cm3'.

If we make 'g/cm3' the default should we also make the the default units when using material.set_density() which I see defaults to None currently?

[shimwell]

wondering if there was a reason that you didn't also add a components argument that gets passed to add_components while you were at it? That would make it truly complete.

I wasn't sure if that would be acceptable so I didn't want it blocking the PR.

I was not sure if it would be acceptable as adding_components currently needs two additional arguments, one for the dict of components and one for the percent_type. The percent_type is a bigger step as it is not a class attribute currently.

So I had a go at reducing components to a single dictionary argument with #3654 but now that PR not going ahead I the way to add components to the init is clearer but it would require adding percent_type as a class attribute.

[shimwell]

ok tests are failing, it looks like many tests assumed the density_units were defaulting to sum so I have opted for this as the default as it was previously the default.

Wondering of we should keep density_units to sum or change them to g/cm3 and update tests accordingly?