Basic Python Classes - Self Function Not Working-CodePudding

I have been learning python for around a week and am trying to set up a basic LRU Cache.

I think I don't fully understand when to use the self command in OOP.

A simplified version of my code is here:

class LRUCache:
    def __init__(self):
        self.cache=[]
    
    def add_to_cache(self, cache, item_to_add):
      pass
    
my_cache = LRUCache()

while True:
     what_to_add = input("What do you want to add?")
     my_cache.add_to_cache(self.cache, what_to_add)

I get an error on the self.cache in the last line, "undefined name self"

I'm not quite sure why I get this- to my understanding my_cache is my object and it should be able to recognize self.cache, and uses that attribute within the add_to_cache function.

I tried searching around both here and on google, but was not able to specifically find what I did wrong.

I appreciate anyone's help or clarity on this situation. I am a beginner and still trying to learn. Thank you!

CodePudding user response：

self represent the current object on which your invoking the method

if you write my_cache.add_to_cache(self.cache, what_to_add)

my_cache gets "transposed" to the self argument in your def add_to_cache(self, cache, item_to_add):

imagine having a function, def test(self): print(self.name) doing my_object.test() correspond to putting my_object instead of self, same as doing test(my_object)

and then it would call my_object.name in your case you either want to do

my_cache.add_to_cache(my_cache.cache, what_to_add)

or better, since you have self, just delete the cache argument and in your function use it like that

def add_to_cache(self, item_to_add):
      cache = self.cache

and you would call it like that

my_cache.add_to_cache(what_to_add)

hope that was clear

CodePudding user response：

In python self use for the simmilar purpouse this keyword use in java.Therefore in this case self.cach indicate that cache list belong to the my_cache object. Therefore in this way you can not access cache list outside of class because python not which object you are refering.You have to move this add_to_cache method to inside of the class. Then it may be look like this.

class LRU_cache:
    def add_to_cache(self,what_to_add):
       self.cache.add(what_to_add)

Then you can call this method refering the my_cache object.

my_cache.add_to_cache(what_to_add)