Editing dict values in a method

Question

I have a program where I am keeping the statistics of objects in the game in a dict, like this:

Weapon = namedtuple("Weapon", ["owned", "damage", "price", "accuracy"])

weapons = {
    "fists":    Weapon(True, 2, None, 75),
    "knife":    Weapon(False, 4, 50, 95),
    "sword":    Weapon(False, 6, 100, 90),
    "pistol":   Weapon(False, 8, 250, 65),
    "rifle":    Weapon(False, 10, 500, 80),
    "rpg":      Weapon(False, 20, 1000, 100)
}

How would I edit The owned value from inside of a function?

Namedtuples are immutable. You could use recordtypes. http://stackoverflow.com/questions/2970608/what-are-named-tuples-in-python — wrdeman, Mar 04 '15 at 19:12
@wrdeman you can use _replace on the namedtuple and re-assign to the dictionary. See my answer — Peter Wood, Mar 04 '15 at 19:15

Boa · Answer 1 · 2015-03-04T19:49:10.070

namedtuple is immutable. Why not use classes? Your code will be cleaner, more organized, modular, and easier to reuse.

class Weapon:
    def __init__(self, owned, damage, price, accuracy):
        self.owned = owned
        self.damage = damage
        self.price = price
        self.accuracy = accuracy

    def flip_weapon_owned_value(self):
        self.owned = False if self.owned else True
        print "\n", self.owned


weapons = {
    'fists' :  Weapon(True, 2, None, 75),
    'knife' :  Weapon(False, 4, 50, 95),
    'sword' :  Weapon(False, 6, 100, 90),
    'pistol' : Weapon(False, 8, 250, 65),
    'rifle' :   Weapon(False, 10, 500, 80),
    'rpg' :     Weapon(False, 20, 1000, 100)
}

> weapons['fists'].flip_weapon_owned_value()
> False

> weapons['fists'].flip_weapon_owned_value()
> True

`self.owned = !self.owned` is simpler. – Peter Wood Mar 05 '15 at 09:52 — Peter Wood, Mar 05 '15 at 09:52

Peter Wood · Answer 2 · 2015-03-04T19:19:20.343

2

A namedtuple allows you to clone it with updated values. See _replace. It starts with an underscore so it won't clash with any of your attribute names.

You need to re-assign this updated clone to the dictionary key:

weapons = ... # as above

def main():
    do_something(weapons)

def do_something(weapons):
    weapons['fists'] = weapons['fists']._replace(owned=False)

edited Mar 04 '15 at 19:19

answered Mar 04 '15 at 19:10

Peter Wood

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I originally tried this and recieved this error message: AttributeError: can't set attribute – Mar 04 '15 at 19:14
Why not replace that entry with a new namedtuple instance, rather than try to modify what seems to be an immutable data type? – BlackVegetable Mar 04 '15 at 19:15
Doh! That's exactly what `_replace` does. My mistake. – BlackVegetable Mar 04 '15 at 19:16
@BlackVegetable No worries, I probably changed the answer when you weren't looking – Peter Wood Mar 04 '15 at 19:16
This defeats the whole purpose of using tuples. – dursk Mar 04 '15 at 19:19
1

@mattm it's not marked private, it's so it doesn't clash with your attributes. – Peter Wood Mar 04 '15 at 19:20
1

Quote: `In addition to the methods inherited from tuples, named tuples support three additional methods and one attribute. To prevent conflicts with field names, the method and attribute names start with an underscore.` – BlackVegetable Mar 04 '15 at 19:20

Editing dict values in a method

2 Answers2