# Immutable User in Python (Enforce Immutability)
"""
Python does NOT have built‑in immutability for custom objects,
but you can enforce it using:
1. __slots__ -> prevents adding new attributes
2. private attributes -> prevents external modification
3. @property (read‑only) -> exposes values safely
4. no setters -> prevents mutation
5. overriding __setattr__ -> blocks changes after initialization
This pattern creates a fully immutable object.
"""
class User:
__slots__ = ("_id", "_name", "_locked")
def __init__(self, id, name):
# Assign internal values
object.__setattr__(self, "_id", id)
object.__setattr__(self, "_name", name)
# Lock the object to prevent further modification
object.__setattr__(self, "_locked", True)
# Read‑only properties
@property
def id(self):
return self._id
@property
def name(self):
return self._name
# Prevent modification after initialization
def __setattr__(self, key, value):
if getattr(self, "_locked", False):
raise AttributeError(f"Cannot modify immutable attribute '{key}'")
object.__setattr__(self, key, value)
# Main program
u = User(42, "Julia")
print("ID:", u.id)
print("Name:", u.name)
# The following lines would raise errors:
# u.id = 100 # Cannot modify immutable attribute 'id'
# u.name = "Tim" # Cannot modify immutable attribute 'name'
# u._id = 100 # Cannot modify immutable attribute '_id'
"""
run:
ID: 42
Name: Julia
"""
