Python：使用 namedtuple._replace 和一个变量作为字段名
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Python: Using namedtuple._replace with a variable as a fieldname
提问by Peter Stewart
Can I reference a namedtuple fieldame using a variable?
我可以使用变量引用namedtuple fieldame 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
回答by Jochen Ritzel
Tuples are immutable, and so are NamedTuples. They are not supposed to be changed!
元组是不可变的，NamedTuples 也是如此。他们不应该被改变！
this_prize._replace(choice = "Yay")calls _replacewith the keyword argument "choice". It doesn't use choiceas a variable and tries to replace a field by the name of choice.
this_prize._replace(choice = "Yay")调用_replace与关键字参数"choice"。它不用choice作变量，而是尝试用 的名称替换字段choice。
this_prize._replace(**{choice : "Yay"} )would use whatever choiceis as the fieldname
this_prize._replace(**{choice : "Yay"} )将使用任何choice作为字段名
_replacereturns a new NamedTuple. You need to reasign it: this_prize = this_prize._replace(**{choice : "Yay"} )
_replace返回一个新的 NamedTuple。您需要重新分配它：this_prize = this_prize._replace(**{choice : "Yay"} )
Simply use a dict or write a normal class instead!
只需使用字典或编写普通类即可！
回答by SilentGhost
>>> 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
