def molWeight(protseq):
    protweight = {"A":89,"V":117,"L":131,"I":131,"P":115,"F":165,
              "W":204,"M":149,"G":75,"S":105,"C":121,"T":119,
              "Y":181,"N":132,"Q":146,"D":133,"E":147,
              "K":146,"R":174,"H":155 }
    totalW = 0
    protseq = protseq.upper() #so proteins in lower case also OK
    for aa in protseq:
        if aa in protweight:
            totalW = totalW + protweight[aa]

    H2O = 18 #weight of water molecule
    totalW = totalW-(H2O*(len(protseq)-1)) #reduce weight for all amino bonds
    return totalW