# Source code for pbxplore.structure.loader

    #! /usr/bin/env python
    # -*- coding: utf-8 -*-

    from __future__ import absolute_import

    # Local module
    from .structure import Chain, Atom
    from .PDB import PDB

    # Conditional import
    try:
        import MDAnalysis
    except ImportError:
        IS_MDANALYSIS = False
    else:
        IS_MDANALYSIS = True

    # Create the __all__ keyword according to the conditional import
    __all__ = ['chains_from_files']
    if IS_MDANALYSIS:
        __all__ += ['chains_from_trajectory']

    def chains_from_files(path_list):
        for pdb_name in path_list:
            pdb = PDB(pdb_name)
            for chain in pdb.get_chains():
                # build comment
                comment = pdb_name
                if chain.model:
                    comment += " | model %s" % (chain.model)
                if chain.name:
                    comment += " | chain %s" % (chain.name)
                yield comment, chain

    def chains_from_trajectory(trajectory, topology):
        universe = MDAnalysis.Universe(topology, trajectory)
        selection = universe.select_atoms("backbone")

        #Initialize structure with the selection
        structure = Chain()
        for atm in selection:
            atom = Atom.read_from_xtc(atm)
            # append structure with atom
            structure.add_atom(atom)

        for ts in universe.trajectory:
            #Update only with new coordinates
            structure.set_coordinates(selection.positions)

            # define structure comment
            comment = "%s | frame %s" % (trajectory, ts.frame)
            yield comment, structure