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PCAP-31-03: How Does Python Handle Multiple Exceptions in Nested Try-Except Blocks?

By: Author Alex Lim

Posted on

Categories Exam

Explore Python’s exception handling in nested try-except blocks, global variables, and assertions. Learn how different error types affect program flow and variable values in this PCAP-31-03 exam question breakdown.

Table of Contents

Question

What is the expected behavior of the following code?

m = 0
def foo(n):
global m
assert m != 0
try:
return 1/n
except ArithmeticError:
raise ValueError

try:
foo(0)
except ArithmetricError:
m += 2
except:
m += 1

A. it outputs 3
B. the code is erroneous and it will not execute
C. it outputs 2
D. it outputs 1

Answer

D. it outputs 1

Explanation

Let’s break down the code and explain its execution step by step:

  1. Initially, `m` is set to 0.
  2. The `foo` function is defined with a parameter `n`. It uses the global variable `m`.
  3. Inside `foo`, there’s an assertion `assert m != 0`. This will raise an AssertionError because `m` is 0 when the function is called.
  4. The main try-except block attempts to call `foo(0)`.
  5. When `foo(0)` is called, it immediately raises an AssertionError due to the assert statement.
  6. The AssertionError is not caught by the first except clause (which catches ArithmeticError), so it falls through to the bare except clause.
  7. In the bare except clause, `m` is incremented by 1, so `m` becomes 1.
  8. The code execution completes, and the final value of `m` is 1.

Key points to note:

  • The AssertionError is raised before the function even attempts the division by zero, so the ValueError in the function is never raised.
  • The spelling of “ArithmeticError” in the outer try-except block is incorrect (it’s spelled “ArithmetricError”), but this doesn’t affect the execution because this except clause is never reached.
  • The bare except clause catches all exceptions not caught by the previous except clauses, including AssertionError.

This question tests understanding of:

  • Global variables
  • Assertions
  • Exception handling with try-except blocks
  • The order of exception handling
  • How nested try-except blocks interact

For the PCAP-31-03 exam, it’s crucial to understand these concepts and how they work together in Python programs.

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.