human
Complete the below
def get_connection(alias=DEFAULT_CONNECTION_NAME, reconnect=False):

    ''''Return a connection with a given alias.'
    '''
 ... Write me a the Python code you requested?
assistant
#Here is the Python code you requested.
    if reconnect:
        disconnect(alias)
    if (alias in _connections):
        return _connections[alias]
    if (alias not in _connection_settings):
        if (alias == DEFAULT_CONNECTION_NAME):
            msg = 'You    have    not    defined    a    default    connection'
        else:
            msg = ('Connection    with    alias    "%s"    has    not    been    defined' % alias)
        raise MongoEngineConnectionError(msg)
    def _clean_settings(settings_dict):
        irrelevant_fields_set = {'name', 'username', 'password', 'authentication_source', 'authentication_mechanism'}
        return {k: v for (k, v) in settings_dict.items() if (k not in irrelevant_fields_set)}
    conn_settings = _clean_settings(_connection_settings[alias].copy())
    is_mock = conn_settings.pop('is_mock', False)
    if is_mock:
        try:
            import mongomock
        except ImportError:
            raise RuntimeError('You    need    mongomock    installed    to    mock    MongoEngine.')
        connection_class = mongomock.MongoClient
    else:
        connection_class = MongoClient
        if (('replicaSet' in conn_settings) and (not IS_PYMONGO_3)):
            connection_class = MongoReplicaSetClient
            conn_settings['hosts_or_uri'] = conn_settings.pop('host', None)
            if isinstance(conn_settings['hosts_or_uri'], list):
                conn_settings['hosts_or_uri'] = ','.join(conn_settings['hosts_or_uri'])
            conn_settings.pop('port', None)
    existing_connection = None
    connection_settings_iterator = ((db_alias, settings.copy()) for (db_alias, settings) in _connection_settings.items())
    for (db_alias, connection_settings) in connection_settings_iterator:
        connection_settings = _clean_settings(connection_settings)
        if ((conn_settings == connection_settings) and _connections.get(db_alias)):
            existing_connection = _connections[db_alias]
            break
    if existing_connection:
        _connections[alias] = existing_connection
    else:
       ...