PCEP Control Flow, Loops, Lists and Logic Practice Test 5 — 15 Questions

Question 1

A program uses a while loop to find the largest number in a list until a negative number is encountered. What is wrong with this code?

numbers = [3, 7, 2, -1, 5]
max_num = 0
i = 0
while numbers[i] >= 0:
    if numbers[i] > max_num:
        max_num = numbers[i]
    i += 1
print(max_num)

Accepted Answer

The loop should continue even when number is negative (skip negatives).. The while loop condition `numbers[i] >= 0` causes the loop to terminate as soon as it encounters a negative number (-1), so it never processes the number 5 at the end of the list. The intended behavior is to skip negative numbers and continue iterating through the entire list to find the largest number among all non-negative values. To fix this, the loop should use a condition that checks the index against the list length (e.g., `i < len(numbers)`) and then skip negative numbers with an `if` statement inside the loop.

Answer

The loop should start with max_num = None.

Answer

The loop should check all numbers until end of list.

Answer

The loop should use a for loop instead.

Question 2

A developer wants to generate a list of squares of integers from 1 to 10 inclusive. Which list comprehension is correct?

Accepted Answer

[x**2 for x in range(1, 11)]. `range(1, 11)` generates integers from 1 to 10 inclusive, and the list comprehension `[x**2 for x in range(1, 11)]` squares each integer, producing the desired list of squares. The `range()` function's stop value is exclusive, so `range(1, 11)` stops at 10, covering all numbers from 1 to 10.

Answer

[x**2 for x in range(11)]

Answer

[x**2 for x in range(10)]

Answer

[x**2 for x in range(1, 10)]

Question 3

A developer needs to check if all elements in a list of integers are even. Which code correctly implements this?

Accepted Answer

all_even = True
for num in mylist:
    if num % 2 != 0:
        all_even = False
        break. It initializes `all_even` to `True`, then iterates through the list. If any element is odd (`num % 2 != 0`), it sets `all_even` to `False` and breaks out of the loop early, which is an efficient and correct way to check that all elements are even.

Answer

all_even = all(num % 2 for num in mylist)

Answer

all_even = any(num % 2 == 0 for num in mylist)

Answer

all_even = False
for num in mylist:
    if num % 2 == 0:
        all_even = True
    else:
        all_even = False

Question 4

Which TWO of the following list operations modify the list in place?

Accepted Answer

mylist.sort(). `mylist.sort()` sorts the list in place, meaning it modifies the original list object without creating a new one. Option E is correct because `mylist.append(5)` adds the element 5 to the end of the list, directly mutating the original list object.

Answer

mylist + [5]

Answer

mylist.copy()

Answer

mylist = mylist + [5]

Question 5

Which THREE of the following are valid ways to iterate over a list?

Accepted Answer

for i in mylist:. Python's `for i in mylist:` syntax directly iterates over each element of the list `mylist`, assigning the element value to the loop variable `i` in each iteration. This is the standard and most Pythonic way to traverse a list.

Answer

foreach i in mylist:

Answer

iter(mylist)

Question 6

A company needs to filter a list of temperatures in Celsius to only those above 0, then convert to Fahrenheit (multiply by 9/5 and add 32). Which code snippet correctly accomplishes this using a list comprehension?

Accepted Answer

[t*9/5+32 for t in temps if t>0]. It uses the standard list comprehension syntax: `[expression for item in iterable if condition]`. Here, `t*9/5+32` is the expression that converts Celsius to Fahrenheit, `for t in temps` iterates over the list, and `if t>0` filters out temperatures at or below zero. This produces a new list containing only the Fahrenheit equivalents of positive Celsius temperatures.

Answer

[t for t in temps if t>0 then t*9/5+32]

Answer

[t*9/5+32 for t in temps if t>0 else 0]

Answer

[t*9/5+32 for t in temps if t>0 else t]

Question 7

A developer writes code to iterate over a list and break when a certain condition is met. Which keyword is used to exit the loop prematurely?

Accepted Answer

break. The `break` keyword is used in Python to immediately exit the nearest enclosing loop (for or while) when a specified condition is met, allowing the program to resume execution at the next statement after the loop. This is the standard mechanism for premature loop termination in Python, as defined in the language specification.

Answer

stop

Answer

exit

Answer

continue

Question 8

A log file processing script uses a while loop to read lines until a specific pattern is found. The code currently hangs. The developer suspects an infinite loop. Which change is most likely to fix the issue?

Accepted Answer

Ensure the condition variable is updated inside the loop. An infinite while loop typically occurs when the condition controlling the loop never becomes false. In a log file processing script, the condition variable (e.g., a line counter or a flag indicating the pattern was found) must be updated inside the loop body. Without that update, the loop condition remains true indefinitely, causing the hang. Adding a `break` statement (option A) would exit the loop unconditionally after the first iteration, which is not the intended fix for a missing update.

Answer

Add a break statement after reading the line

Answer

Increase the sleep time in the loop

Answer

Replace while with for loop

Question 9

A program needs to print the index and value of each item in a list named 'items'. Which code snippet correctly does this?

Accepted Answer

Both A and C are correct. Both Option A and Option C are valid code snippets that correctly print the index and value of each item in the list. Option A uses the clean, Pythonic enumerate() function. Option C uses range(len(items)) to iterate by index. Since both are correct, the best answer is B, which correctly identifies that both A and C are correct. Option D is incorrect because items.index(item) can fail with duplicate values and is inefficient.

Answer

for i, item in enumerate(items): print(i, item)

Answer

for i in range(len(items)): print(i, items[i])

Answer

for item in items: print(items.index(item), item)

Question 10

What is the output of the code?

numbers = [1, 2, 3, 4]
result = [x**2 for x in numbers if x % 2 == 0]
print(result)

Accepted Answer

[4, 16]. The list comprehension `[x**2 for x in numbers if x % 2 == 0]` iterates over `numbers`, filters for even numbers (2 and 4) using the condition `x % 2 == 0`, and squares each selected element. Squaring 2 gives 4, squaring 4 gives 16, so the result is `[4, 16]`. Option B is correct.

Answer

[2, 4]

Answer

[1, 9]

Answer

[2, 4, 16]

Question 11

A network engineer writes a script to validate IP addresses. The script checks each octet and prints 'Valid' if all octets are between 0 and 255, otherwise 'Invalid'. However, the script always prints 'Invalid' for valid IPs. The code uses a for loop with an else clause. Which logical error is likely?

Accepted Answer

The for loop's else clause executes when the loop completes without break, but the engineer expects else to run when break occurs. In Python, a `for` loop's `else` clause executes only when the loop completes normally (i.e., without hitting a `break`). The engineer likely intended the `else` to run when an invalid octet is found (triggering a `break`), but instead the `else` runs when all octets are valid and the loop finishes without breaking, causing the script to always print 'Invalid' when the validation logic is inverted.

Answer

The list of octets is not properly split

Answer

The condition uses 'or' instead of 'and'

Answer

The else clause is indented incorrectly

Question 12

Which of the following best describes the behavior of the 'range' function in a for loop?

Accepted Answer

It generates a sequence of numbers from start to stop exclusive. The built-in `range()` function in Python generates an immutable sequence of numbers from the start value (default 0) up to, but not including, the stop value. When used in a `for` loop, it yields each number in the sequence one at a time, making it ideal for iterating a fixed number of times. The stop value is exclusive, meaning the loop body does not execute for the stop value itself.

Answer

It returns a list of numbers with a default step of 0

Answer

It can only be used with integers

Answer

It generates a list of numbers from start to stop inclusive

Question 13

What does the following code print?

x = 10
if x > 5:
    if x > 15:
        print("A")
    else:
        print("B")
else:
    print("C")

Accepted Answer

B. The code first checks if x > 5, which is true because x = 10. Then it checks if x > 15, which is false, so the else branch of the inner if-else executes, printing 'B'. The outer else is skipped entirely.

Answer

No output

Answer

C

Answer

A

Question 14

A developer is writing a function that takes a list of numbers and returns the sum of all even numbers. Which two code snippets correctly implement this function? (Select two.)

Accepted Answer

def sum_even(nums): total=0; for n in nums: if n%2==0: total+=n; return total. It initializes a total variable to 0, iterates over each number in the list, checks if it is even using the modulo operator (n % 2 == 0), and adds the number to the total. This correctly accumulates the sum of all even numbers and returns the final total.

Answer

def sum_even(nums): return [n for n in nums if n%2==0]

Answer

def sum_even(nums): total=0; for i in range(len(nums)): if nums[i]%2==0: total+=nums[i]*2; return total

Answer

def sum_even(nums): total=0; for n in nums: if n%2==1: total+=n; return total

Question 15

Which two of the following are valid ways to create a list with elements 1, 2, 3? (Select two.)

Accepted Answer

list = list(range(1, 4)). `list(range(1, 4))` creates a list from the range object that generates numbers 1, 2, and 3 (the `range` function stops before the stop value 4). This is a common Python idiom for converting a range into a list.

Answer

list = [1, 2, 3]]

Answer

list = (1, 2, 3)

Answer

list = [1; 2; 3]