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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def from_filenames(poscar_filenames, transformations=None, extend_collection=False):
 """ 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__. """

        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)