Build the initial data dictionary to store the values

def setup_keys(self):
        """ Build the initial data dictionary to store the values
        """

        discovery_methods = {}
        discovery_years = {}
        nan_list = []

        # Initial Loop to get keys
        for planet in self.planet_list:
            if 'Solar System' in planet.params['list'] and self.skip_solar_system_planets:
                continue
            try:
                discovery_methods[planet.discoveryMethod] += 1
            except KeyError:
                discovery_methods[planet.discoveryMethod] = 1

            try:
                discovery_years[planet.discoveryYear] += 1
            except KeyError:
                discovery_years[planet.discoveryYear] = 1

            if planet.discoveryMethod is np.nan:
                nan_list.append(planet)

        self.nan_list = nan_list

        return discovery_years