Question 1

__repr__ vs __str__

Accepted Answer

When you type an object in the REPL or call repr(), Python calls __repr__. When you call str() or print(), Python calls __str__ (falling back to __repr__ if __str__ is not defined). The convention: __repr__ should return a string that, if passed to eval(), would recreate the object. __str__ can be friendlier. If you only define one, define __repr__ - it covers both use cases.

Question 2

Instance variable vs class variable

Accepted Answer

count is a class variable - it is shared across all instances. Each __init__ call increments Counter.count (not self.count). After creating two instances, Counter.count is 2. If you had written self.count += 1 instead, it would create a separate instance variable on each object and leave Counter.count at 0.

Question 3

__init__ basics

Accepted Answer

__init__ is the initializer - it runs when you create an instance. self refers to the new instance being created. self.name = name stores the argument as an instance attribute. Accessing d.name later returns whatever was passed at construction time.

Question 4

Shadowing a class variable with an instance variable

Accepted Answer

Assigning to a.debug creates an instance variable on 'a' that shadows the class variable. Python's attribute lookup checks the instance first, then the class. So a.debug finds the instance variable and returns True. b.debug has no instance variable, so Python falls back to Config.debug which is still False. Config.debug itself is also still False - the class variable was never changed. This shadowing behavior trips up many developers who expect assignment to one instance to affect all instances. If you want to change the class variable, you must write Config.debug = True explicitly.

Question 5

__init__ with a default parameter

Accepted Answer

Default parameter values in __init__ work the same as in any Python function. When 'a = Car('Toyota')' omits the year argument, self.year gets the default value 2020. When 'b = Car('Honda', 2023)' provides year explicitly, 2023 overrides the default and self.year is 2023. Each instance stores its own year attribute independently - a.year and b.year are separate values on separate objects.