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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 inventory(self):
 """ Create an inventory structure and returns a dict. .. code-block:: yaml ungrouped: vars: foo: bar hosts: instance-1: instance-2: children: $child_group_name: hosts: instance-1: instance-2: $group_name: hosts: instance-1: ansible_connection: docker instance-2: ansible_connection: docker :return: str """

        dd = self._vivify()
        for platform in self._config.platforms.instances:
            for group in platform.get('groups', ['ungrouped']):
                instance_name = platform['name']
                connection_options = self.connection_options(instance_name)
                molecule_vars = {
                    'molecule_file':
                    "{{ lookup('env', 'MOLECULE_FILE') }}",
                    'molecule_ephemeral_directory':
                    "{{ lookup('env', 'MOLECULE_EPHEMERAL_DIRECTORY') }}",
                    'molecule_scenario_directory':
                    "{{ lookup('env', 'MOLECULE_SCENARIO_DIRECTORY') }}",
                    'molecule_yml':
                    "{{ lookup('file', molecule_file) | molecule_from_yaml }}",
                    'molecule_instance_config':
                    "{{ lookup('env', 'MOLECULE_INSTANCE_CONFIG') }}",
                    'molecule_no_log':
                    "{{ lookup('env', 'MOLECULE_NO_LOG') or not "
                    "molecule_yml.provisioner.log|default(False) | bool }}"
                }

                # All group
                dd['all']['hosts'][instance_name] = connection_options
                dd['all']['vars'] = molecule_vars
                # Named group
                dd[group]['hosts'][instance_name] = connection_options
                dd[group]['vars'] = molecule_vars
                # Ungrouped
                dd['ungrouped']['vars'] = {}
                # Children
                for child_group in platform.get('children', []):
                    dd[group]['children'][child_group]['hosts'][
                        instance_name] = connection_options

        return self._default_to_regular(dd)