PCEP Control Flow, Loops, Lists and Logic — Timed 20 Questions

Question 1

A programmer needs to check if at least one element in a list of booleans flags is True. Which expression correctly does this?

Accepted Answer

any(flags). The built-in `any()` function returns `True` if at least one element in the iterable is truthy. For a list of booleans, this correctly checks if any element is `True`. Option A, `True in flags`, only checks for the exact boolean `True`, but if the list contained truthy non-boolean values (e.g., integers), it would not work. Since the question specifies a list of booleans, both work conceptually, but `any()` is the standard, more robust approach and is the intended correct answer here.

Answer

True in flags

Answer

all(flags)

Answer

flags.any()

Question 2

Which three of the following expressions evaluate to True? (Choose three.)

Accepted Answer

3 in [1,2,3] and 4 not in [1,2,3]. '3 in [1,2,3]' is True, '4 not in [1,2,3]' is True, so True and True yields True. Option D: 'a' in 'abc' is True, and because the left operand is True, the 'or' short-circuits and the expression is True. Option E: (True and False) is False, (False or True) is True, so False or True yields True. Therefore, three options evaluate to True.

Answer

(10 > 5) and (5 < 3)

Answer

not (0 or 1)

Question 3

A developer is troubleshooting a loop that terminates earlier than expected. The code is: i = 0; while i < 5: if i == 3: break; print(i); i += 1. What is the output?

Accepted Answer

0 1 2. The loop starts with i=0 and increments i by 1 each iteration. When i reaches 3, the break statement executes, immediately terminating the loop. Therefore, only i values 0, 1, and 2 are printed, making option D correct.

Answer

0 1 2 3 4

Answer

0 1 2 3

Answer

0 1

Question 4

Which TWO of the following are true about Python's if statement?

Accepted Answer

An if statement can have multiple elif blocks.. Python's if statement allows multiple elif blocks to check additional conditions after the initial if condition. This enables a chain of conditional checks, and each elif is evaluated only if all previous conditions were False. The elif clause is a contraction of 'else if' and is a unique feature of Python's syntax.

Answer

if statements cannot be nested.

Answer

An if statement must have a corresponding else clause.

Answer

The condition must be enclosed in parentheses.

Question 5

A developer writes a loop to sum numbers from 1 to 10. The code outputs 55, but the expected sum is 55. However, the loop uses a range that includes 0. Which range should be used to achieve the correct sum?

Accepted Answer

range(1,11). (range(1,11)) is correct because range(start, stop) generates numbers from start inclusive to stop exclusive. To sum numbers 1 through 10, the range must start at 1 and end at 11 (so 10 is included). The loop that used range(0,11) included 0, but since adding 0 does not change the sum, the output was still 55 — however, the question asks for the range that achieves the correct sum without including unnecessary values.

Answer

range(0,11)

Answer

range(0,101)

Answer

range(1,10)

Question 6

A programmer needs to iterate over a list of strings and print each string in uppercase. Which loop correctly accomplishes this?

Accepted Answer

for i, item in enumerate(mylist): print(item.upper()). Both Option A and Option D correctly iterate over the list and print each string in uppercase. Option A uses enumerate to get each item and calls item.upper() with parentheses, printing the result. Although it introduces an unused index variable i, it still works correctly. Option D uses range(len(mylist)) to access each element by index and prints mylist[i].upper(). Option B fails because it does not print the result; it only reassigns the variable. Option C omits the parentheses on upper(), printing the method object instead of the string.

Answer

for item in mylist: item = item.upper()

Answer

for item in mylist: print(item.upper)

Question 7

A programmer writes code that uses a while loop to process user input until the user types 'exit'. The code currently prints 'Done' after the loop, but it never exits. What is the most likely cause?

Accepted Answer

The variable controlling the loop is not updated inside the loop. If the variable controlling the loop (e.g., the user's input) is never updated inside the while loop, the loop condition will never become false, causing an infinite loop. In this scenario, the programmer likely reads input once before the loop but does not call input() again inside the loop to update the variable, so the loop never sees the 'exit' value.

Answer

The loop condition is 'while True'

Answer

The print statement is indented incorrectly

Answer

The input function is called outside the loop

Question 8

A list of numbers is defined as nums = [1, 2, 3, 4, 5]. Which expression returns the last element?

Accepted Answer

nums[-1]. Python uses zero-based indexing, so the first element is at index 0 and the last element is at index -1. Negative indices count from the end of the list, so nums[-1] directly accesses the last element (5) without needing to know the list length.

Answer

nums[5]

Answer

nums[0]

Answer

nums[-2]

Question 9

A list contains strings and numbers: items = ['apple', 10, 'banana', 20]. A programmer wants to create a new list that contains only the strings. Which approach is correct?

Accepted Answer

[item for item in items if isinstance(item, str)]. The `isinstance(item, str)` function is the recommended way to check if an item is a string because it handles inheritance and is more readable. Option C, `type(item) == str`, also works in this case but is not considered the best practice for type checking in Python, especially when dealing with subclasses. Option A uses `isdigit()`, which only works for strings that represent digits, not all strings. Option B uses `type(item) is 'str'`, which compares the type to a string literal, which is incorrect.

Answer

[item for item in items if item.isdigit()]

Answer

[item for item in items if type(item) is 'str']

Answer

[item for item in items if type(item) == str]

Question 10

A developer writes the following code snippet:
for i in range(3):
    for j in range(2):
        if i == j:
            break
    else:
        print(i, 'outer')
What is the output?

Accepted Answer

2 outer. The code uses nested loops with a `for-else` construct. The `else` block executes only if the inner loop completes without a `break`. When `i == j`, the `break` exits the inner loop, skipping the `else`. For `i=0`, `j=0` triggers `break`; for `i=1`, `j=1` triggers `break`; for `i=2`, the inner loop runs `j=0,1` without any `i==j` (since 2 != 0 and 2 != 1), so the `else` executes, printing `2 outer`. Thus, only option B is correct.

Answer

0 outer
2 outer

Answer

0 outer
1 outer
2 outer

Answer

No output

Question 11

Given the code:
x = [1, 2, 3]
y = x
y.append(4)
print(x)
What is the output?

Accepted Answer

[1, 2, 3, 4]. In Python, variables hold references to objects, not the objects themselves. When `y = x` is executed, both `x` and `y` point to the same list object in memory. The `y.append(4)` method modifies that shared list in-place, so the change is reflected when `x` is printed, outputting `[1, 2, 3, 4]`.

Answer

Error

Answer

[1, 2, 3]

Answer

[1, 2, 3, 4, 5]

Question 12

A programmer wants to create a list of even numbers from 0 to 10 inclusive. Which list comprehension is correct?

Accepted Answer

[x for x in range(0,11) if x%2==0]. It uses `range(0,11)` to generate numbers from 0 to 10 inclusive, and the condition `if x%2==0` selects only even numbers (where the remainder when divided by 2 is 0). This matches the requirement exactly.

Answer

[x for x in range(0,10) if x%2==0]

Answer

[x for x in range(0,11) if x%2]

Answer

[x for x in range(0,11) if x%2==1]

Question 13

What is the output of the code?

Accepted Answer

0 1 2 4. The code uses a for loop with range(5) to iterate over numbers 0 through 4. Inside the loop, an if statement checks if the current number equals 3; if true, the continue statement skips the remainder of the current iteration and moves to the next iteration. Therefore, when i is 3, the print(i) statement is skipped, but the loop continues with i=4, printing 4. Thus, the output is '0 1 2 4' (each on a new line). Option C correctly lists the printed values as 0, 1, 2, and 4.

Answer

No output

Answer

0 1 2 3 4

Answer

0 1 2 4 5

Question 14

A developer runs main.py and gets True. They then modify config.py by adding `allowed_ports.append(22)` and run main.py again without restarting the interpreter. What is the output?

Accepted Answer

True. Python imports modules only once per interpreter session; subsequent imports use the cached module object. Since `config.py` was already imported, modifying the file does not affect the already-loaded list object in memory. The `allowed_ports` list remains unchanged, so the condition that originally returned `True` still holds.

Answer

False

Answer

None

Answer

Error

Question 15

Which THREE of the following are valid ways to create a list with elements 10, 20, 30?

Accepted Answer

my_list = [x for x in (10,20,30)]. Options A, B, and E are all valid ways to create a list with the elements 10, 20, 30. Option A uses a list comprehension to iterate over a tuple and produce the list. Option B uses the list() constructor with a tuple as the single iterable argument. Option E is the most direct way: a list literal. Options C and D are invalid: C because list() requires a single iterable, not multiple positional arguments; D because Python list elements must be separated by commas, not semicolons.

Answer

my_list = list(10, 20, 30)

Answer

my_list = [10; 20; 30]

Question 16

Which TWO of the following code snippets will print the numbers 0, 1, 2, 3, 4?

Accepted Answer

for i in range(0,5): print(i). `range(0,5)` generates the sequence 0, 1, 2, 3, 4. The `range()` function with two arguments (start, stop) produces numbers from start inclusive up to, but not including, stop. Therefore, iterating with `for i in range(0,5): print(i)` prints exactly 0 through 4.

Answer

for i in range(5+1): print(i)

Answer

for i in range(0,5,2): print(i)

Answer

for i in range(1,6): print(i)

Question 17

Which THREE of the following are valid list operations?

Accepted Answer

my_list.extend([5,6]). The `extend()` method appends each element of the iterable (here, the list `[5,6]`) to the end of the original list, modifying it in place. This is a valid list operation in Python that adds multiple elements at once.

Answer

my_list.add(5)

Answer

my_list.push(5)

Question 18

You are working on a network automation script that reads a configuration file containing firewall rules. Each rule is a dictionary with keys 'source_ip', 'dest_ip', 'action'. The script must iterate over the rules and print all rules where action is 'allow'. However, the script is not printing any output even though there are allow rules in the file. The code snippet is:

rules = [{'source_ip':'10.0.0.1','dest_ip':'10.0.0.2','action':'allow'},
         {'source_ip':'10.0.0.2','dest_ip':'10.0.0.3','action':'deny'}]
for rule in rules:
    if rule('action') == 'allow':
        print(rule)

What is the most likely cause of the problem?

Accepted Answer

The developer used rule('action') instead of rule['action']. In Python, dictionary values are accessed using square brackets (e.g., rule['action']) or the .get() method, not parentheses. Using parentheses like rule('action') attempts to call the dictionary as a function, which raises a TypeError and prevents the script from executing, so no output is printed even though allow rules exist.

Answer

The dictionary does not have an 'action' key

Answer

The developer used rule['action'] instead of rule.get('action')

Answer

The for loop syntax is incorrect; it should be for rule in rules:

Question 19

You are writing a script to parse a log file. Each line in the log contains a timestamp and a message separated by a colon. You need to extract only the messages that contain the word 'ERROR'. The script uses a list comprehension to filter lines. However, the script crashes with a 'ValueError: not enough values to unpack' when processing some lines. The code is:

lines = ['2024-01-01 12:00:00: INFO: all good', '2024-01-01 12:01:00: ERROR: something wrong']
errors = [msg for timestamp, msg in line.split(': ') for line in lines if 'ERROR' in msg]

What is the correct fix?

Accepted Answer

Rewrite as: [msg for line in lines if 'ERROR' in line for msg in [line.split(': ')[1]]]. It properly separates the filtering and unpacking steps. The original code attempts to unpack each line into timestamp and msg using `line.split(': ')`, but some lines may not contain exactly two parts after splitting (e.g., if the colon is missing or there are extra colons), causing a ValueError. Option D first filters lines containing 'ERROR', then safely extracts the message part by splitting and taking index [1] inside a nested comprehension, avoiding the unpacking error.

Answer

Rewrite as: [line for line in lines if 'ERROR' in line]

Answer

Change the list to a dictionary

Answer

Swap the order of the for clauses to: [msg for line in lines for timestamp, msg in line.split(': ') if 'ERROR' in msg]

Question 20

Arrange the steps to handle an exception in Python using try-except.

Accepted Answer

try block, then except block, then else block, then finally block. Exception handling wraps risky code in try, catches exceptions with except, and optionally includes else and finally.

Answer

try block, then except block, then finally block, then else block

Answer

try block, then else block, then except block, then finally block

Answer

except block, then try block, then else block, then finally block