Question

I made a simple code to demonstrate and understand classes – however when I run this, my lists show that they are empty, containing “None” values instead of the strings that the user enters as names.

#Static methods do not require the object to be initiated. Can be remotely accessed from outside the function .

#Counting critters and remote access.

class Orc (object):

    total = 0       

    def get_score (self):
        print "The number of orcs the orc factory has made is",Orc.total   

    def __init__ (self):
        Orc.total += 1
        name =  raw_input ("I am a critter by the name of:\n")


#Creating 10 Orcs 


list = []

for i in range (4):    list[i] = list.append(Orc.get_score(Orc()))  

print "You have created 4 Orcs!" print "The name of your first orc is",list[0] print "The name of your fourth orc is", list[3]

Answer 1

There are a few errors in your code. First in the way you use lists. Second, in the way you call methods on your objects. The combination of errors explains why you have a list of None at the end.

List name

list = []

Don’t name a list list. It is already the name of, well…, the list class, i.e. in Python you can do my_list = [] or my_list = list() with the exact same effect.

You want to call your list something meaningful, like orc_list

List Insertion

for i in range (4):
    orc_list[i] = orc_list.append(...)

orc_list.append does what it says: it appends an element to the given list. However, it does not return anything. So what your code is doing is

1. taking an empty list
2. setting i to 0
3. inserting what you pass to append at the end of the list
4. inserting None at index i and thus overriding what you did in 3.
5. incrementing i
6. going back to 3.

You want to simply use orc_list.append(...)

Method Call

Orc.get_score(Orc())

I imagine you are getting confused by the self argument. In a class, Python will automatically pass the instance you are working on as the self argument. You don’t need to provide that argument.

You want to write

Orc().get_score()

This creates an Orc object, and then calls get_score on it. Python ‘injects’ the Orc instance you have created into get_score for you.

Method Return

We’re now down to

orc_list.append(Orc().get_score())

which is equivalent to

score = Orc().get_score()
orc_list.append(score)

The problem is that there is no return statement in get_score. This means that python will return None when you call that method. Which means that you are appending None to your list.

You want to have

def get_score(self):
    print "The number of orcs the orc factory has made is", Orc.total
    return Orc.total

Static behaviour

If you really wanted to have a method not bound to an instance of the Orc class, you could use either a class method or a static method.

In your case, you do not need to do anything to the class object, so your choice would be to use a static method.

You would declare

@staticmethod
def get_score():
    print "The number of orcs the orc factory has made is", Orc.total

You would then call that method using Orc.get_score()