CODEWITHSUNDEEP
pythonlistmethods
Yotam
Yotam

Reputation: 10685

defining a method inside a class in python

I'm taking my first steps in python programming, I have a class named node which holds a list of nodes (I think that legal) named sons. I tried to create a function that returns the length of the list but it fails. Here is my code: 

class node:
    name="temp"
    ID=-1
    abstract="a short description"
    text="the full description"
    sons=[]
    def sLen(none):
        print ("hello")
        return len(self.sons)

and here is the error:

NameError: global name 'self' is not defined

if I try to remove the self:

NameError: global name 'self' is not defined

Clearly I have misunderstood something, but what?

Upvotes: 1

Views: 132

Answers (3)

Savino Sguera
Savino Sguera

Reputation: 3572

The first argument of a class method is always a reference to "self".

Possibly you will find interesting answers here too: What is the purpose of self?.

Quoting the most important bit:

Python decided to do methods in a way that makes the instance to which the method belongs be passed automatically, but not received automatically: the first parameter of methods is the instance the method is called on.

If you look for a more thorough discussion about classes definition in python, of course the official documentation is the place to start from: http://docs.python.org/tutorial/classes.html.

Upvotes: 1

Andrey Agibalov
Andrey Agibalov

Reputation: 7694

class node:
    name="temp"
    ID=-1
    abstract="a short description"
    text="the full description"
    sons=[]
    def sLen(self): # here
        print ("hello")
        return len(self.sons)

n = node()
n.sons = [1, 2, 3]
print n.sLen()

Upvotes: 3

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798616

You called the first argument to the method none, not self.

return len(none.sons)

Upvotes: 0

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