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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 get_cantera_mass_fraction(self, species_conversion=None):
 """Get the mass fractions in a string format suitable for input to Cantera. Arguments: species_conversion (`dict`, optional):
 Mapping of species identifier to a species name. This argument should be supplied when the name of the species in the ChemKED YAML file does not match the name of the same species in a chemical kinetic mechanism. The species identifier (the key of the mapping) can be the name, InChI, or SMILES provided in the ChemKED file, while the value associated with a key should be the desired name in the Cantera format output string. Returns: `str`: String of mass fractions in the ``SPEC:AMT, SPEC:AMT`` format Raises: `ValueError`: If the composition type is ``'mole fraction'`` or ``'mole percent'``, the conversion cannot be done because no molecular weight information is known Examples: 'H2:2.2525e-04, O2:4.4775e-03, Ar:9.9530e-01' 'h2:2.2525e-04, o2:4.4775e-03, Ar:9.9530e-01' 'h2:2.2525e-04, o2:4.4775e-03, Ar:9.9530e-01' """

        if self.composition_type in ['mole fraction', 'mole percent']:
            raise ValueError('Cannot get mass fractions from the given composition.\n'
                             '{}'.format(self.composition)
                             )
        else:
            return self.get_cantera_composition_string(species_conversion)