class AddressBook:

    def __init__(self):
        self.address_dict = {}

    def __setitem__(self, key, value):
        self.address_dict[key] = value

    def __getitem__(self, item):
        return self.address_dict[item]

    def delete(self, name):
        del self.address_dict[name]

    def save(self):
        with open('address_dict.txt', 'tw', encoding='utf-8') as a:
            for i in self.address_dict.keys():
                a.write(f'{i}: {self.address_dict[i]}' + '\n')

a = AddressBook()
a['Vasya'] = 'Moskwa'
a['Petya'] = 'Piter'
a.delete('Vasya')
a.save()