Accessing an attribute using a variable in Python

56
votes

How do I reference this_prize.left or this_prize.right using a variable?

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", this_prize.choice)

AttributeError: 'Prize' object has no attribute 'choice'
2
python
FYI - You can skip the collections import and just use a dictionary to do the same thing: >>> this_prize = {"left": "FirstPrize", "right":"FirstPrize"} >>> this_prize[choice] >'FirstPrize' - Jason Coon
Related: stackoverflow.com/questions/1167398/… - S.Lott

2 Answers

94
votes

The expression this_prize.choice is telling the interpreter that you want to access an attribute of this_prize with the name "choice". But this attribute does not exist in this_prize.

What you actually want is to return the attribute of this_prize identified by the value of choice. So you just need to change your last line...

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)
89
votes
getattr(this_prize, choice)

From http://docs.python.org/library/functions.html#getattr:

getattr(object, name) returns the value of the named attribute of object. name must be a string