def add_site_property(self, property_name, values):
        """
        Adds a property to a site.

        Args:
            property_name (str): The name of the property to add.
            values (list): A sequence of values. Must be same length as
                number of sites.
        """
        if len(values) != len(self.sites):
            raise ValueError("Values must be same length as sites.")
        for site, val in zip(self.sites, values):
            site.properties[property_name] = val
Adds a property to a site.

        Args:
            property_name (str): The name of the property to add.
            values (list): A sequence of values. Must be same length as
                number of sites.