Type Error in IG Helmholz free energy due to certain properties specified

[jranalli]

Source: ig.py - L1742 and ig2.py - L1278

Basically, what's happening is that it's possible to reach that point without p having been defined when certain property sets are specified. Basically, when pairs not containing p are sent to _argparse, it can return None for p, which causes the division to fail.

The relevant pairs are:

• Td, Tv, dh, vh, de, ve
  • These are all actually the same pair (T & d) because h and e are replaced by T early on.
  • One possible fix for this one is just calculating values for it, e.g. p = d * R * T on ig.py#L262 ig2.py#L247
• ds, vs
  • Similar, you might insert p = d * R * T in ig.py#L235 and ig2.py#L220

As a more general issue, the fact that _argparse can return nulls could lead to future similar bugs. I would possibly suggest that the appropriate algebraic form of the ideal gas law should be inserted into each case of _argparse generally to ensure that T, p, and d are fully populated. In this case though, the issue is just that f specifically relies on a completed value of p. The other places where it looks like this would be an issue right now are:

• s+p could leave d blank
• T+p could leave d blank