Section 1/5Public (default)

Public (default)

No underscore = public. Anyone can read or write it.

Access Modifiers

Access modifiers control which parts of your program can read or change an object's data. Python uses naming conventions rather than keywords.

Public (default)

class Person:
    def __init__(self, name):
        self.name = name  # public — accessible anywhere

p = Person("Alice")
print(p.name)  # → Alice  ✓

No underscore = public. Anyone can read or write it.

Protected (_single underscore)

class Employee:
    def __init__(self, salary):
        self._salary = salary  # protected convention

e = Employee(50000)
print(e._salary)  # → 50000 (works, but signals caution)

A single leading underscore is a convention. Python will not prevent access, but it signals to other developers: "this is internal — do not use directly." In IB exams, _attribute = protected.

Private (__double underscore)

class Employee:
    def __init__(self, pin):
        self.__pin = pin   # private — name-mangled

e = Employee(1234)
# e.__pin            # → AttributeError!
# e._Employee__pin   # the mangled name (avoid using this)

Double underscore triggers name mangling. Python renames the attribute to _ClassName__attribute internally, making accidental access from outside the class raise an AttributeError.

Comparison: Java vs Python

Java uses keywords: public, protected, private — enforced by the compiler
Python uses naming conventions: name, _name, __name — enforced by convention
IB questions may use either language — the concept is the same

# Task: Apply Python's access modifier conventions to Employee.
#
# 1. Change 'salary' to a PROTECTED attribute: _salary
#    (use a single underscore — accessible but signals "internal use")
# 2. Change 'pin' to a PRIVATE attribute: __pin
#    (double underscore — name-mangled, not easily accessible outside)
# 3. Keep 'name' as public (no underscore needed)
class Employee:
    def __init__(self, name, salary, pin):
        self.name   = name
        self.salary = salary   # make this protected: _salary
        self.pin    = pin      # make this private: __pin
    def get_details(self):
        return f"{self.name} earns £{self._salary}"  # already uses _salary
e = Employee("Bob", 50000, 1234)
print(e.name)       # public — should work fine
print(e._salary)    # protected — works, but signals "be careful"
# print(e.__pin)    # private — this line would raise AttributeError
print(e.get_details())

Output:

Click "Check" to run your code.

Access Modifiers

Public (default)

Protected (_single underscore)

Private (__double underscore)

Comparison: Java vs Python

Your Task

Public (default)

Access Modifiers

Public (default)

Protected (_single underscore)

Private (__double underscore)

Comparison: Java vs Python

Your Task

Output: