Explore a tricky Python dictionary scenario from the PCAP-31-03 exam. Learn about key-value pairs, set operations, and exception handling in this expert analysis.
Table of Contents
Question
What is the expected behavior of the following code?
d = {'1': '1', '2', '3'}
try:
d['1'] = d['3']
except BaseException as error:
print(type(error))
A. it outputs
B. the code is erroneous and it will not execute
C. it outputs
D. it outputs
Answer
The correct answer to this question is C. The code will output <class ‘KeyError’>.
Explanation
Let’s break down the code and explain why:
1. Dictionary initialization:
d = {‘1’: ‘1’, ‘2’, ‘3’}
This creates a dictionary with one key-value pair (‘1’: ‘1’) and two additional keys (‘2’ and ‘3’) without values. In Python, when you include items without colons in a dictionary literal, they are treated as keys with None as their value.
2. The try block:
d[‘1’] = d[‘3’]
This line attempts to assign the value of d[‘3’] to d[‘1’]. However, ‘3’ is a key in the dictionary without an associated value (it’s implicitly None).
3. KeyError exception:
When you try to access a key that doesn’t exist in a dictionary, Python raises a KeyError. In this case, trying to access d[‘3’] will raise a KeyError because ‘3’ is a key without an explicit value.
4. Exception handling:
The except block catches BaseException, which is the base class for all built-in exceptions in Python. KeyError is a subclass of BaseException, so it will be caught by this except block.
5. Output:
print(type(error))
This line prints the type of the caught exception, which is KeyError.
Therefore, when this code is executed, it will output:
<class ‘KeyError’>
This question tests your understanding of Python dictionaries, exception handling, and the behavior of KeyError exceptions. It’s important to remember that in Python dictionaries, keys without explicit values are treated as having None as their value, and attempting to access such keys will raise a KeyError.
Python Institute PCAP-31-03 certification exam practice question and answer (Q&A) dump with detail explanation and reference available free, helpful to pass the Python Institute PCAP-31-03 exam and earn Python Institute PCAP-31-03 certification.