AttributeError: Object Missing Instance Attribute

Why This Happens

Instance attributes are created by assignment with self.attr = value in __init__. If you forget self, you create a local variable. If __init__ conditionally sets attributes, some instances may lack them.

The Problem

class Counter:
    def __init__(self, start):
        count = start  # Missing self!

    def increment(self):
        self.count += 1

The Fix

class Counter:
    def __init__(self, start):
        self.count = start

    def increment(self):
        self.count += 1

Step-by-Step Fix

1. 1

   Check __init__ for self

   Verify all attribute assignments use self.attribute = value.

2. 2

   Check for typos

   Ensure the attribute name in __init__ matches the name used elsewhere.

3. 3

   Initialize all attributes

   Set default values for all attributes in __init__.