Code Explanation:
1️⃣ Creating the Class
class A:
This creates a class named A.
The class is designed so that repeated calls to A() return the same object.
This pattern is commonly known as the Singleton pattern.
2️⃣ Creating the Class Variable
obj = None
obj is a class variable.
Initially, it contains:
obj → None
It will later store the single instance of class A.
3️⃣ Defining __new__()
def __new__(cls):
__new__() is responsible for creating and returning an object.
It runs before __init__().
Here, cls refers to the class A.
So conceptually:
cls → A
4️⃣ Checking Whether an Object Already Exists
if cls.obj is None:
Python checks whether obj is still None.
Initially:
cls.obj → None
Therefore, the condition is:
True
So Python enters the if block.
5️⃣ Creating the First Object
cls.obj = super().__new__(cls)
super().__new__(cls) calls the standard object creation mechanism.
A new instance of A is created and stored in:
cls.obj
Now:
cls.obj → first A object
6️⃣ Returning the Object
return cls.obj
The newly created object is returned.
Therefore:
a = A()
makes a point to that object.
Conceptually:
a ─────┐
↓
A object
↑
cls.obj
7️⃣ Creating b
b = A()
Python calls A.__new__() again.
This time:
cls.obj is None
is False, because an object already exists.
Therefore, this block is skipped:
cls.obj = super().__new__(cls)
Instead, Python directly executes:
return cls.obj
So b receives the same object.
8️⃣ Comparing a and b
print(a is b)
The is operator checks whether two variables refer to the exact same object in memory.
Here:
a ─────┐
↓
A object
↑
b ─────┘
Both point to the same instance.
Therefore:
a is b
is:
True
🔄 Complete Execution Flow
a = A()
↓
__new__()
↓
obj is None? → YES
↓
Create object
↓
Store in cls.obj
↓
Return object
↓
a points to object
b = A()
↓
__new__()
↓
obj is None? → NO
↓
Return existing object
↓
b points to SAME object
🎯 Final Output
True
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