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AttributeError: missing self

🐛 Fix the bug Topic: oop Difficulty: medium Free

What this problem practises

Object-oriented bugs hide in state: class attributes shared by every instance, mutable defaults declared in __init__ signatures, and methods that mutate self when the caller expected a copy.

This is a fix-the-bug problem: a short program is given in its broken state, and the task is to repair the code so it produces the required output. The interactive editor runs your fixed version in the browser and checks it for you — no setup, no local interpreter.

Difficulty: medium — expect to hold two interacting rules in your head at once, such as a boundary combined with a mutation.

The challenge

This program crashes with AttributeError when calling show(). Fix __init__ so it prints Priya.

The code runs in PyDebug’s in-browser compiler. Open the problem, run the snippet, watch the exact error or output, and keep iterating until it is right. Signed-in solves count toward XP and your daily streak.

The error it raises

Run the broken snippet and Python stops with this exact error: AttributeError / TypeError on instance method without self. Match it to the Python errors guide, then repair the line that produced it — knowing the message is half the fix.

The snippet

The interactive editor pre-fills exactly this code, broken and ready to repair:

class Student:
    def __init__(self, name):
        name = name
    def show(self):
        print(self.name)
s = Student('Priya')
s.show()

Understand the rule

Unlike Java or C++, Python never injects an implicit `this` keyword inside class methods. Every regular instance method must declare `self` as its first parameter AND prefix instance attributes with `self.` when reading or updating object state.

How to trace it

Calling `obj.method()` on an instance automatically binds `obj` and passes it as the first positional argument.
If the method signature forgot `self`, Python raises `TypeError` because one more argument arrived than parameters were declared.
If `__init__` assigned `count = 0` instead of `self.count = 0`, `count` stayed a local variable and vanished when `__init__` returned.
Later reading `self.count` fails with `AttributeError` because the attribute was never attached to the instance dictionary.

Common wrong fixes

Writing `count = 0` inside `__init__`, creating a throwaway local variable instead of an instance attribute `self.count`.
Calling another method on the same class as `helper()` instead of `self.helper()`, triggering `NameError`.
Adding `@staticmethod` just to silence the missing `self` error when the method actually needs per-instance state.

Rule to remember

Every instance method takes `self` first, and every per-object variable must be stored and read through `self.attr_name`.

Solve it in the interactive editor →

Keep going

Python debugging guide — a systematic method for finding bugs like this one fast.
Browse every oop problem in this topic.
Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.