import re


def get_sandwich(seq, aa="FYW"):
    """
    Add sandwich counts based on aromatics.

    Parameters:
        seq: str, peptide sequence
        aa: str,
             amino acids to check fo rsandwiches. Def:FYW
    """
    # count sandwich patterns between all aromatic aminocds and do not
    # distinguish between WxY and WxW.
    pattern = re.compile(r"(?=([" + aa + "][^" + aa + "][" + aa + "]))")
    return len(re.findall(pattern, seq))