Writes the BIF data into a file

        Parameters
        ----------
        filename : Name of the file

        Example
        -------
        >>> from pgmpy.readwrite import BIFReader, BIFWriter
        >>> model = BIFReader('dog-problem.bif').get_model()
        >>> writer = BIFWriter(model)
        >>> writer.write_bif(filname='test_file.bif')

def write_bif(self, filename):
        """
        Writes the BIF data into a file

        Parameters
        ----------
        filename : Name of the file

        Example
        -------
        >>> from pgmpy.readwrite import BIFReader, BIFWriter
        >>> model = BIFReader('dog-problem.bif').get_model()
        >>> writer = BIFWriter(model)
        >>> writer.write_bif(filname='test_file.bif')
        """
        writer = self.__str__()
        with open(filename, 'w') as fout:
            fout.write(writer)