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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 make_app():
 """Helper function that creates a plnt app."""

    from plnt import Plnt

    database_uri = os.environ.get("PLNT_DATABASE_URI")
    app = Plnt(database_uri or "sqlite:////tmp/plnt.db")
    app.bind_to_context()
    return app