Encountered "self" in Python

Question

I have just started learning python and I am trying to write a binary search tree. Eclipse does not show any errors but when I try to run there is ann error

Encountered "self" at line 5

Line 5 is:

"self.left = left"

What is the problem? Is my way of writing code okey? I have just starded python.

class Node:

    def _init_(self, data, left=None, right=None):
        self.data = data
        self.left = left
        self.right = right 

    def add_node(self, data):
        if self.data is None:
            node = Node(data)
            self = node
        if self.data > data:
            self.add_node(self.left, data)
        else:
            self.add_node(self.right, data)

    def print_nodes(self):
        if self.left is not None:
            self.print_nodes(self.left)
        print(self);
        if self.right is not None:
            self.print_nodes(self.right)

    def _str_(self):
        print(self.data)

class binary_tree:

    def _init_(self):
        self.root = None

    def getRoot(self):
        return self.root

    def add(self, data):
        self.root.add_node(data)

    def print_all(self):
        self.root.print_nodes();

Are you sure that's the exact code you are executing? I do not see any syntax errors. Incidentally, you probably want to write `__init__` and `__str__` instead of `_init_` and `_str_`. — fjarri, Jan 29 '16 at 00:00
One thing: Maybe you want `__init__` instead of `_init_`. See also [this question](http://stackoverflow.com/questions/625083/python-init-and-self-what-do-they-do). — e0k, Jan 29 '16 at 00:00
I am using eclipse and all I see is this error on left down size in red font colour. Console does not show anything — Mateusz, Jan 29 '16 at 00:05
When I run "python3 binarytree.py " in console then it does nothing — Mateusz, Jan 29 '16 at 00:08
Did you try creating any objects of the classes you defined? — TigerhawkT3, Jan 29 '16 at 00:14
Of course it does nothing - at least nothing you can see. Your code defines two classes and that's all. Why do you think something should happen? — Matthias, Jan 29 '16 at 00:17
I think eclipse does not know it is supposed to use python or something ... maybe try using idle or something easier for now ... I think eclipse may be confusing you — Joran Beasley, Jan 29 '16 at 00:17
Yeah, I would avoid using Eclipse. Probably not time for you to jump into vim, but any other edit will probably serve you better than Eclipse for Python development. I highly recommend learning nano/emacs/vim at some point however. — Alex Alifimoff, Jan 29 '16 at 00:19
Ok, so how to fix it to be able to run it and create example tree object? — Mateusz, Jan 29 '16 at 11:40

score 1 · Accepted Answer · answered Jan 29 '16 at 13:46

here a few fix to your code

class Node:

    def __init__(self, data, left=None, right=None):
        self.data  = data
        self.left  = left
        self.right = right 

    def add_node(self, data):
        if self.data > data:
            if self.left is None:
                self.left = Node(data)
            else:
                self.left.add_node(data)
        elif self.data < data:
            if self.right is None:
                self.right = Node(data)
            else:
                self.right.add_node(data)

    def print_nodes(self):
        if self.left is not None:
            self.left.print_nodes()
        print(self);
        if self.right is not None:
            self.right.print_nodes()

    def __str__(self):
        return str(self.data)

class binary_tree:

    def __init__(self):
        self.root = None

    def getRoot(self):
        return self.root

    def add(self, data):
        if self.root is None:
            self.root = Node(data)
        else:
            self.root.add_node(data)

    def print_all(self):
        if self.root is None:
            print("Empty tree")
        else:
            self.root.print_nodes()

as mention before the special method of python are __init__ and __str__, all magic method start and end with a __.

I fix your add_node because your recursive call were wrong, went you do self.add_node(self.left,data) the self instance is implicitly pass as the first argument to that function, self.left is the second and data the third but as defined add_node only take 2 argument so that is a error, so in this case if you want to call the add_node of self.left that is done by self.left.add_node and the same apply to every other call to a method of a class

take a look at:

a first look at classes

basic customization and magic methods

here sample usage of this tree

>>> tree = binary_tree()
>>> tree.print_all()
Empty tree
>>> tree.add(23)
>>> tree.print_all()
23
>>> tree.add(10)
>>> tree.add(42)
>>> tree.print_all()
10
23
42
>>> root = tree.root
>>> root.data
23
>>> root.right
<__main__.Node object at 0x0000000003559160>
>>> root.right.data
42
>>> root.left
<__main__.Node object at 0x0000000003577080>
>>> root.left.data
10
>>>

Other thing is that in python you dot need to define getter or setter unless you want to control what and how a attribute is set or return it in a especial way that is different to the actual object.

run this in the IDLE of python or in interactive mode as python3 -i binarytree.py or in your favorite interprete of python.

Encountered "self" in Python

1 Answers1