python计算蛋白质的质量

#!/usr/bin/python3
#-*- coding:utf-8 -*-
"计算蛋白质的质量"
table = {
    ‘A‘:   71.03711,
‘C‘:   103.00919,
‘D‘:  115.02694,
‘E‘:   129.04259,
‘F‘:   147.06841,
‘G‘:   57.02146,
‘H‘:   137.05891,
‘I‘:   113.08406,
‘K‘:   128.09496,
‘L‘:   113.08406,
‘M‘:   131.04049,
‘N‘:   114.04293,
‘P‘:   97.05276,
‘Q‘:   128.05858,
‘R‘:   156.10111,
‘S‘:   87.03203,
‘T‘:   101.04768,
‘V‘:   99.06841,
‘W‘:   186.07931,
‘Y‘:   163.06333
}
import sys
#f=open(‘./protein.txt‘, ‘r‘)
f=open(sys.argv[1])
string =f.read()
weight = 0
for i in string:
    if i in table.keys():
        weight += table[i]
print (weight)
f.close()