CODEWITHSUNDEEP
pythondata-structuressingly-linked-list
Mihir Shah
Mihir Shah

Reputation: 31

I am getting a missing positional argument error.(linked list in python)

code:

class node:
    def __init__(self,data):
        self.data=data
        self.next=None

class linkedlist:
    def __init__(self):
        self.head=None

def printlist(self):
    temp=self.head
    while(temp):
        print(temp.data,end=" ")
        temp=temp.next

def insert_at_start(self,new_data):
    new_node=node(new_data)
    if self.head==None:
        new_node=self.head
    else:
        new_node.next=self.head
        self.head=new_node

l1=linkedlist()
insert_at_start(1)
insert_at_start(5)
insert_at_start(1)
insert_at_start(7)
insert_at_start(5)

l1.printlist()

error: Traceback (most recent call last): File "linkedlist.py", line 65, in insert_at_start(1) TypeError: insert_at_start() missing 1 required positional argument: 'new_data'

Upvotes: 1

Views: 447

Answers (2)

Mustafa Aydın
Mustafa Aydın

Reputation: 18315

First you have the indentation problem that those 2 functions (printlist and insert_at_start) should be methods, so indent them to lie in the linkedlist class. Also two more errors: one is, you need the call

l1.insert_at_start(..)

i.e. the method call on the instance. And the other is a logical error that resides in the lines of:

if self.head == None:
    new_node = self.head

When .head does not exist yet, don't you think .head should be the one assigned to the new_node?

Also note that l1 is probably one of the most confusing variable names ever existed, please change it; and PascalCase your class names.

Upvotes: 1

Gabio
Gabio

Reputation: 9504

You have an indentation problem: insert_at_start is not a method of linkedlist class because it is defined outside of the class scope and that's why it requires 2 args.

Try this instead:

class linkedlist:
    def __init__(self):
        self.head=None

    def printlist(self):
        temp=self.head
        while(temp):
            print(temp.data,end=" ")
            temp=temp.next

    def insert_at_start(self,new_data):
        new_node=node(new_data)
        if self.head==None:
            new_node=self.head
        else:
            new_node.next=self.head
            self.head=new_node

l1=linkedlist()
l1.insert_at_start(1)
l1.insert_at_start(5)
l1.insert_at_start(1)
l1.insert_at_start(7)
l1.insert_at_start(5)
l1.printlist()

Upvotes: 1

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