convert + to ++ and - to -- in load4

[bmaranville]

No description provided.

[pkienzle]

I wouldn't bother with the flag. It'll error out if the flag is False, so it's not useful to reset it.

If you do want to keep it use "HALFPOL" rather than "HALPOL".

[pkienzle]

Maybe want to warn if half-polarization is detected? Probably not.

We could check if halfpol*2 is already defined before promoting so we don't overwrite an existing ++ or –– cross-section, but I think that this is unlikely enough that we can blow it off.

The halfpol*2 is slightly magical. It may be cleaner to just write:

if '+' in data_by_xs:
    data_by_xs['++'] = data_by_xs.pop('+')
if '-' in data_by_xs:
    data_by_xs['--'] = data_by_xs.pop('-')

Or in anticipation of some other halfpol syntax:

_KEY_MAP = {'+': '++', '?+': '++', '+?': '++', '-': '--', '?-': '--', '-?': '--'}
for old, new in _KEY_MAP.items():
    if value := data_by_xs.pop(old, None):
        data_by_xs[new] = value

[glass-ships]

Worth revisiting?

Implement half-polarized probe, that sums e.g. ++ and +- theory xs to compare to + summed data

possibly related?

[bmaranville]

Agreed: this is a half-measure that can be abandoned in favor of the more rigorous solution being worked on.