新手出现问题，请大神请教！

源代码：from prettytable import PrettyTable
mark=PrettyTable()
field=['name','protein','Va','Vc','Ca','Fe']
person1=['spinach',2600,487,32,66,3]
person2=['eggplant',1100,8,5,24,1]
person3=['radish',900,3,21,36,1]
person4=['rape',1800,103,36,108,1]
mark.field_names=field
mark.add_row(person1)
mark.add_row(person2)
mark.add_row(person3)
mark.add_row(person4)
protein=[]
for i in range(1,10,1):
    if not int(protein)>1500:
        protein.append(protein[i][2])
print protein
出现：
Traceback (most recent call last):
  File "C:\Users\Administrator\Desktop\李昊恩Python\test6.19待解决", line 15, in <module>
    if not int(protein)>1500:
TypeError: int() argument must be a string or a number, not 'list'

if not int(protein)>1500:这句错了，空list无法转成int，你想要做什么讲一下。