For example I would like to perform some simple calculations on the coordinates of a set of selected atoms, and I see many functions that take a "sel" argument, but I can't seem to find documentation on exactly what that argument is expected to contain, or the function that would return such a selection list (is it even a list) of objects.
If we are talking about the the 'sel' argument given to many of the functions in Midas/__init__.py, that argument is usually "polymorphic", and can be any one of these:
-- an atom specifier (e.g. "#1@ca")
-- a list/tuple of Atoms/Residues/Molecules (homogeneous list/tuple though)
-- a set of Atoms/Residues/Molecules (also homogenous, and unlike the list/tuple the set has to be at the right "level" for the function called [e.g. Atoms for distance])
-- a Selection/OSLSelection (which Tom mentioned)
--Eric
Eric Pettersen
UCSF Computer Graphics Lab