Name mangling in Python - Step-by-Step Execution

Concept Flow - Name mangling

Define class with __private attribute

↓

Create instance of class

↓

Access __private attribute inside class method

↓

Access __private attribute outside class

↓

Python changes __private to _ClassName__private

↓

Access succeeds using mangled name

Name mangling changes __private names inside classes to _ClassName__private to avoid accidental access from outside.

Execution Sample

Python

class MyClass:
    def __init__(self):
        self.__secret = 42

obj = MyClass()
print(obj._MyClass__secret)

This code shows how Python changes __secret to _MyClass__secret and how to access it.

Execution Table

Step	Action	Variable/Attribute	Value	Note
1	Define class MyClass	MyClass	class object	Class created with __secret attribute
2	Create instance obj	obj	MyClass instance	obj.__secret is not directly accessible
3	Inside __init__, set self.__secret	obj.__secret	42	Name mangled to obj._MyClass__secret internally
4	Try print(obj.__secret)	obj.__secret	AttributeError	Direct access fails, attribute is mangled
5	Print obj._MyClass__secret	obj._MyClass__secret	42	Access succeeds using mangled name

💡 Execution stops after printing the mangled attribute value 42

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5
obj.__secret	undefined	undefined	42 (mangled as _MyClass__secret)	42
obj._MyClass__secret	undefined	undefined	42	42

Key Moments - 2 Insights

Why can't we access obj.__secret directly?

Because Python changes __secret to _MyClass__secret internally (see step 4 in execution_table), so obj.__secret does not exist.

How does Python prevent accidental access to private attributes?

By name mangling: it renames __secret to _ClassName__secret, making it harder to access from outside (see step 3 and 5).

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 4 when trying to print obj.__secret?

A It raises AttributeError

B It prints 42

C It prints None

D It prints _MyClass__secret

💡 Hint

Check step 4 in execution_table where direct access to obj.__secret fails

At which step is the private attribute actually set inside the object?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look at step 3 where self.__secret is assigned the value 42

If the class name changes to YourClass, what would be the mangled name for __secret?

A _MyClass__secret

B _YourClass__secret

C __secret

D _secret

💡 Hint

Name mangling uses _ClassName__attribute format, see concept_flow and execution_table steps

Concept Snapshot

Name mangling in Python:
- Attributes starting with __ are renamed internally.
- Format: __attr becomes _ClassName__attr.
- Prevents accidental external access.
- Access with obj._ClassName__attr if needed.
- Not true private, just name changed.

Full Transcript

Name mangling is a Python feature that changes attribute names starting with double underscores inside classes. When you write __secret inside a class named MyClass, Python changes it to _MyClass__secret internally. This helps avoid accidental access from outside the class. For example, setting self.__secret = 42 inside __init__ actually creates obj._MyClass__secret. Trying to access obj.__secret directly causes an error because that name does not exist. To access the value, you use obj._MyClass__secret. This is not true privacy but a way to reduce naming conflicts. If the class name changes, the mangled name changes accordingly.