如何检查输入是否与数组中的值匹配

Question

这是我到目前为止编写的代码。正如您所看到的，如果您运行代码，我遇到了最后6行及其功能的问题。

kegsize = input('Please enter keg size. Litres: ')
print (kegsize, 'Litres')

netpurchasecost = input('Please enter net purchase cost. GBP: ')
print ('£', netpurchasecost)

abv = input('Please enter Alcohol by Volume. %: ')
print (abv, '%')

gp = input('Please enter Gross Profit Percentage. %: ')
print (gp, '%')

opt = print('These are the Portion Size options (imperial measurements), 1/3, 1/2, 2/3, 1')
portionsize = input('Please choose Portion Size: ')
if portionsize != ['1/3' , '1/2' , '2/3' , '1']:
    print('Please enter a Portion Size from the list')
else:
    print(portionsize)

无论我输入的部分大小是＆＃39; 1/3＆＃39;，＆＃39; 1/2＆＃39;，＆＃39; 2/3＆＃39;或者＆＃39; 1＆＃39; shell仍将输出＆＃39;请从列表中输入部分大小＆＃39;。