How to use the eccodes.codes_count_in_file function in eccodes

def __init__(self, input_bufr_file, warn_about_bufr_size=True,
                 expand_flags=False, expand_strings=False, verbose=False):
        #  #[
        print('opening BUFR file: ', input_bufr_file)

        # open the BUFR file
        self.fd = open(input_bufr_file,'r')

        # extract the number of BUFR messages from the file
        self.num_msgs =  eccodes.codes_count_in_file(self.fd)

        print('self.num_msgs = ', self.num_msgs)

        # not yet used
        self.verbose = verbose
    
        # keep track of which bufr message has been loaded and
        # decoded from this file
        self.msg_index = -1
        self._bufr = -1

        # allow manual choice of tables
        #self.table_b_to_use = None
        #self.table_c_to_use = None
        #self.table_d_to_use = None
        self.tables_dir = None