使用 nametuple._replace 和变量作为字段名

Question

我可以使用变量引用命名元组字段吗？

from collections import namedtuple
import random 

Prize = namedtuple("Prize", ["left", "right"]) 

this_prize = Prize("FirstPrize", "SecondPrize")

if random.random() > .5:
    choice = "left"
else:
    choice = "right"
    
#retrieve the value of "left" or "right" depending on the choice
print "You won", getattr(this_prize,choice)
 
#replace the value of "left" or "right" depending on the choice
this_prize._replace(choice  = "Yay") #this doesn't work

print this_prize

Answer 1

元组是不可变的，NamedTuples 也是如此。它们不应该被改变！

this_prize._replace(choice = "Yay") 使用关键字参数 "choice" 调用 _replace。它不使用 choice 作为变量，并尝试用 choice 名称替换字段。

this_prize._replace(**{choice : "Yay"} ) 将使用任何 choice ，因为字段名

_replace 返回一个新的 NamedTuple。您需要重新分配它： this_prize = this_prize._replace(**{choice : "Yay"} )

只需使用字典或编写普通类即可！

Answer 2

>>> choice = 'left'
>>> this_prize._replace(**{choice: 'Yay'})         # you need to assign this to this_prize if you want
Prize(left='Yay', right='SecondPrize')
>>> this_prize
Prize(left='FirstPrize', right='SecondPrize')         # doesn't modify this_prize in place