def ReverseComplement(barcode):
    """
    barcode: (str) just "A""C""T""G"
    We return reverse complement: ACCAGT -> ACTGGT
    """
    revc_bc = ""
    barcode = barcode.upper()
    transl_d = {"A":"T","C":"G","T":"A","G":"C"}
    for char in barcode:
        if char not in ["A","C","T","G"]:
            raise Exception("char {} not in ACTG as expected".format(char))
        else:
            revc_bc += (transl_d[char])

    return revc_bc[::-1]