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常见错误

Mistake 1: Forgetting super().__init__()​

# Wrong — parent attributes never initialised
class Manager(Employee):
    def __init__(self, name, id, salary, bonus):
        self._name = name       # duplicated parent logic
        self._bonus = bonus
# Correct
class Manager(Employee):
    def __init__(self, name, id, salary, bonus):
        super().__init__(name, id, salary)
        self._bonus = bonus

Mistake 2: Passing self to super().__init__()​

# Wrong — Python passes self automatically
super().__init__(self, name, id, salary)
# Correct
super().__init__(name, id, salary)

Mistake 3: Wrong method signature when overriding​

# Parent
def display_info(self):
    return f"Name: {self._name}"

# Wrong — extra parameter changes signature
def display_info(self, extra):
    return f"Name: {self._name}, {extra}"

The overridden method must have exactly the same name and parameters as the parent.

Mistake 4: Not calling super().method() when required​

If the question asks the child method to include parent behaviour plus new behaviour, you must call super().method().

# Wrong — reinventing parent logic
def get_info(self):
    return f"Manufacturer: {self._manufacturer}, Model: {self._model}, Blades: {self._blades}"
# Correct — reuse parent then extend
def get_info(self):
    parent_info = super().get_info()
    return f"{parent_info}, Blades: {self._blades}"

Mistake 5: Wrong attribute naming​

# Wrong — accessing parent private attribute incorrectly
print(self._Manufacturer__manufacturer)

Parent attributes accessed via self._attr in child class (same as parent, assuming single underscore convention).

Mistake 6: Misaligned constructor parameters​

Parent constructor expects (name, id) but child passes (id, name). The parameter order in super().__init__() must exactly match the parent's parameter list.

Mistake 7: Forgetting to convert types when reading from file​

# Wrong — all values treated as strings
age = parts[2]   # "25" instead of 25
# Correct — convert numeric fields
age = int(parts[2])

Mistake 8: Wrong indentation after if / elif in file reading​

Objects created inside if block but not accessible outside. Use a list to store all objects.

# Wrong — obj not accessible after if
if type_flag == "P":
    obj = Parent(...)
else:
    obj = Child(...)
# Correct — store in list
objects = []
if type_flag == "P":
    objects.append(Parent(...))
else:
    objects.append(Child(...))