Python · Theory

Constructors in Python

Theory

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Constructors in Python

__init__ is the initializer most people mean by constructor. It runs when you create the object: s = Student("Asha", 12). Inside, self.name = name stores fields. You do not call __init__ yourself. Student(...) does it. Forget self on the first parameter and you get TypeError.

__new__ actually creates the instance — advanced, skip unless they ask. Viva signature: def __init__(self, name, roll). Then one object on the board: print(s.name) → Asha.

Constructors in Python — output — 4. Box(4) calls __init__ and sets side.

Exam tip

__init__(self, ...) + one Student example.

Example

# Constructor
class Box:
    def __init__(self, side):
        self.side = side

b = Box(4)
print(b.side)

Constructors in Python — output: 4. Box(4) calls __init__ and sets side.

Short notes

Def__init__ runs on create.
Ruleself first. Store attributes.
RememberDon’t call __init__ by hand.

Python · Theory

Constructors in Python

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Theory

56/268

Constructors in Python

__new__ actually creates the instance — advanced, skip unless they ask. Viva signature: def __init__(self, name, roll). Then one object on the board: print(s.name) → Asha.

Constructors in Python — output — 4. Box(4) calls __init__ and sets side.

Exam tip

__init__(self, ...) + one Student example.

Example

# Constructor
class Box:
    def __init__(self, side):
        self.side = side

b = Box(4)
print(b.side)

Constructors in Python — output: 4. Box(4) calls __init__ and sets side.

Short notes

Def__init__ runs on create.
Ruleself first. Store attributes.
RememberDon’t call __init__ by hand.

Constructors in Python

Example

Short notes

Questions

Constructors in Python

Example

Short notes

Questions