def count_records(fpath):
    """Quickly count headers in FASTA file.

    Args:
        fpath (str): path to input FASTA file.
    
    Returns:
        int: number of headers (lines starting with ">")
    """
    rc = 0
    with open(fpath, 'r') as IH:
        for line in IH:
            if '>' == line[0]:
                rc += 1
    return rc
