Handling AttributeError for Missing Attributes
Exhibit
class BankAccount:
def __init__(self, owner, balance=0):
self.owner = owner
self.__balance = balance
def deposit(self, amount):
self.__balance += amount
def withdraw(self, amount):
if amount <= self.__balance:
self.__balance -= amount
else:
print('Insufficient funds')
def get_balance(self):
return self.__balance
account = BankAccount('Alice', 100)
print(account.__balance)Refer to the exhibit. What is the output when this code is executed?
Quick Answer
The answer is AttributeError. This error occurs because the code attempts to access an undefined attribute `balance` on a `BankAccount` instance, yet the class only defines `__init__` and `deposit` methods without ever setting a `balance` attribute. In Python, when you try to access a missing attribute on an object, the interpreter raises an `AttributeError` rather than returning `None` or a default value—this is a fundamental rule of Python’s attribute lookup mechanism. On the PCAP exam, this concept tests your understanding of object attribute management and error handling, often appearing in questions that trick you into assuming attributes are automatically created by method names. A common trap is thinking that a method named `deposit` implies a `balance` attribute exists, but Python requires explicit assignment in `__init__` or elsewhere. Memory tip: “No attribute, no default—AttributeError is the result.”
⚠ Common exam trap
Python Institute often tests the misconception that accessing a missing attribute in Python returns a default value like `None` or `0`, when in fact it raises an `AttributeError` unless the class defines `__getattr__` or `__getattribute__`.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
AttributeError
The code attempts to access the attribute `balance` on an instance of `BankAccount`, but the class uses `__balance` (double underscore) in the `__init__` method, which triggers Python's name mangling. The attribute is actually stored as `_BankAccount__balance`. Therefore, `balance` does not exist on the instance, and accessing it raises an `AttributeError`. In Python, accessing a non-existent attribute raises an error rather than returning a default value.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
AttributeError
Why this is correct
Name mangling prevents direct access to __balance.
- ✗
0
Why it's wrong here
No, it raises an error.
- ✗
None
Why it's wrong here
Error is raised, not None.
- ✗
100
Why it's wrong here
Direct access is not possible due to name mangling.
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Same concept, more angles
1 more way this is tested on PCAP
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. What will happen when the code is executed?
medium- A.It prints None
- B.It raises a TypeError
- ✓ C.It raises an AttributeError
- D.It prints 10
Why C: The code attempts to call a method or access an attribute that does not exist on the object. In Python, when you try to access an attribute or method that is not defined on an object, an AttributeError is raised. Option C is correct because the exhibit shows an attempt to call a non-existent method or attribute on an instance, which triggers AttributeError.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCAP practice question is part of Courseiva's free Python Institute certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCAP exam.