Property decorator usage in Python - Step-by-Step Execution

Concept Flow - Property decorator usage

Define class with private attribute

↓

Define @property method

↓

Access property: calls getter method

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Define @property.setter method

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Assign to property: calls setter method

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Property value updated internally

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Access property again to get updated value

The flow shows how a class uses @property to create a getter and setter for a private attribute, allowing controlled access and update.

Execution Sample

Python

class Person:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value

p = Person('Alice')
print(p.name)
p.name = 'Bob'
print(p.name)

This code creates a Person class with a private _name attribute and uses @property to get and set the name safely.

Execution Table

Step	Action	Variable/Attribute	Value	Output
1	Create Person instance with name 'Alice'	p._name	'Alice'
2	Access p.name (calls getter)	p.name	'Alice'	Alice
3	Assign p.name = 'Bob' (calls setter)	p._name	'Bob'
4	Access p.name again (calls getter)	p.name	'Bob'	Bob
5	End of program			Execution stops

💡 Program ends after printing updated property value.

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
p._name	undefined	'Alice'	'Bob'	'Bob'
p.name (getter)	undefined	'Alice'	'Bob'	'Bob'

Key Moments - 3 Insights

Why do we use _name instead of name inside the class?

We use _name as a private attribute to avoid direct access. The property methods control how name is accessed or changed, as shown in steps 1 and 3 of the execution_table.

What happens when we assign p.name = 'Bob'?

The setter method is called, which updates the private _name attribute. This is shown in step 3 where p._name changes to 'Bob'.

Why does print(p.name) call a method instead of accessing a variable?

Because of the @property decorator, p.name calls the getter method, which returns the private _name value. This is shown in steps 2 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of p._name after step 3?

A 'Bob'

B 'Alice'

C undefined

D None

💡 Hint

Check the 'Variable/Attribute' and 'Value' columns at step 3 in execution_table.

At which step does the getter method return 'Alice'?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for when p.name is accessed and output is 'Alice' in execution_table.

If we remove the @name.setter method, what happens when we assign p.name = 'Bob'?

A It updates p._name to 'Bob' anyway

B It silently ignores the assignment

C It raises an AttributeError

D It creates a new attribute p.name

💡 Hint

Think about how property setters control assignment, and what happens if setter is missing.

Concept Snapshot

Use @property to create a getter method for a private attribute.
Use @propertyname.setter to create a setter method.
Accessing the property calls the getter.
Assigning to the property calls the setter.
This controls attribute access safely and cleanly.

Full Transcript

This visual execution shows how the property decorator works in Python. We start by creating a class with a private attribute _name. The @property decorator makes a method act like a readable attribute. When we access p.name, it calls the getter method and returns _name. The @name.setter decorator allows us to assign to p.name, which calls the setter method and updates _name. The execution table traces these steps, showing how p._name changes from 'Alice' to 'Bob'. Key moments clarify why we use a private attribute and how the getter and setter methods work. The quiz tests understanding of variable values at each step and what happens if the setter is missing.