code: def from_filenames(poscar_filenames, transformations=None,
                         extend_collection=False):
          
          tstructs = []
          for filename in poscar_filenames:
              with open(filename, "r") as f:
                  tstructs.append(TransformedStructure
                                  .from_poscar_string(f.read(), []))
          return StandardTransmuter(tstructs, transformations,
                                    extend_collection=extend_collection)
docs: Convenient constructor to generates a POSCAR transmuter from a list of
          POSCAR filenames.
  
          Args:
              poscar_filenames: List of POSCAR filenames
              transformations: New transformations to be applied to all
                  structures.
              extend_collection:
                  Same meaning as in __init__.