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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 featurizer(topfile):
 r""" Featurizer to select features from MD data. Parameters topfile : str or mdtraj.Topology instance path to topology file (e.g pdb file) or a mdtraj.Topology object Returns ------- feat : :class:`Featurizer <pyemma.coordinates.data.featurization.featurizer.MDFeaturizer>` Examples -------- Create a featurizer and add backbone torsion angles to active features. Then use it in :func:`source` or .. autoclass:: pyemma.coordinates.data.featurization.featurizer.MDFeaturizer :members: :undoc-members: .. rubric:: Methods .. autoautosummary:: pyemma.coordinates.data.featurization.featurizer.MDFeaturizer :methods: .. rubric:: Attributes .. autoautosummary:: pyemma.coordinates.data.featurization.featurizer.MDFeaturizer :attributes: """

    from pyemma.coordinates.data.featurization.featurizer import MDFeaturizer
    return MDFeaturizer(topfile)