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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 open_notebook(self, filenames=None):

 """Open a notebook from file."""

        if not filenames:
            filenames, _selfilter = getopenfilenames(self, _("Open notebook"),
                                                     '', FILES_FILTER)
        if filenames:
            for filename in filenames:
                self.create_new_client(filename=filename)