MTH 4300 Diagnostic Exam

This quiz assesses your readiness based on the Python programming course you completed. It covers core concepts that will be essential as we transition to C++. Answer all questions to the best of your ability — this is not graded, but it will help your instructor understand where to focus early instruction.

Section 1: Code Tracing

For each question, predict the exact output the program would print.

Q1.

What does this program print? Write the output exactly as it would appear.

x = 10

def mystery(n):
    if n <= 1:
        return 1
    return n * mystery(n - 1)

print(mystery(5))
print(x)

Q2.

What does this program print?

nums = [1, 2, 3, 4, 5]
result = []
for i in range(len(nums)):
    if nums[i] % 2 == 0:
        result.append(nums[i] * 2)
    else:
        result.append(nums[i])
print(result)

Q3.

What does this program print? Pay close attention to what is modified and where.

def add_item(lst, item):
    lst.append(item)
    item = 99

my_list = [1, 2, 3]
my_num = 7
add_item(my_list, my_num)
print(my_list)
print(my_num)

Q4.

What does this program print? Trace through each iteration.

total = 0
for i in range(1, 6):
    for j in range(i):
        total += 1
print(total)

Q5.

What does this program print?

a = 5
b = 2
print(a // b)
print(a % b)
print(a / b)

Section 2: Short Written Answer

Answer in your own words. Complete sentences are encouraged.

Q6.

Consider the two functions below. Both are called with x = [1, 2, 3]. After calling each function, does the original list change? Explain why or why not for each case.

def func_a(lst):
    lst.append(4)

def func_b(lst):
    lst = [10, 20, 30]

Q7.

In your own words, what is a class? What is the difference between a class and an instance of a class? Give a real-world analogy to support your answer.

Q8.

What does the self parameter represent in a Python method? Why does every instance method need it as its first parameter?

Section 3: Write a Function

Write working Python code. You may use any built-in data types, but the restrictions noted in each question apply.

Q9.

Write a function second_largest(nums) that takes a list of integers and returns the second largest value. Do not use Python's built-in sorted() or max(). Assume the list has at least two distinct values.

def second_largest(nums):
    # your code here

Q10.

Write a function count_words(sentence) that takes a string and returns a dictionary mapping each word to the number of times it appears. Treat the input as all lowercase with no punctuation.

count_words("the cat sat on the mat")
# → {"the": 2, "cat": 1, "sat": 1, "on": 1, "mat": 1}

def count_words(sentence):
    # your code here

Section 4: Debugging

Each function below contains a bug. Identify the bug and write a corrected version.

Q11.

The function below is supposed to return the sum of all numbers from 1 to n (inclusive), but it has a bug. Identify the bug and write the corrected version.

def sum_to_n(n):
    total = 0
    i = 1
    while i < n:
        total += i
        i += 1
    return total

Describe the bug:

Corrected code:

def sum_to_n(n):
    # your fix here

Q12.

The function below is supposed to remove all negative numbers from a list and return the result. It has a bug. Identify it and write the corrected version.

def remove_negatives(nums):
    for n in nums:
        if n < 0:
            nums.remove(n)
    return nums