restype_lig and other text fields converted to float

[xrobin]

I just ran into an issue with 1HDQ, where the ligand, INF, is wrongly converted to a floating point number representation of positive infinity, which causes issues downstream.

plipcmd -i 1hdq -x

And then:

>>> import plip.modules.plipxml as plip
>>> report = plip.PLIPXML("report.xml")
>>> print(report.bsites['INF:A:1308'].hydrophobics[0].restype_lig)
inf
>>> print(type(report.bsites['INF:A:1308'].hydrophobics[0].restype_lig))
<type 'float'>

When dumped into json the ligand name becomes Infinity (without quotes) instead of 'INF' (with quotes) so I cannot get the ligand back. When dumped with ujson an OverflowError is raised.

There are other ligand names which can be interpreted as numbers, for instance 1ONY has a ligand named 588, and a ligand named NAN exists, although it isn't used in any PDB entry so far.

[ssalentin]

Merged pull request.