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

Question 1

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). Option B (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 2

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()). Option A is correct because it uses a for loop with enumerate to iterate over the list, and calls the string method upper() (with parentheses) to convert each item to uppercase before printing. This ensures each string is properly transformed and output.

Answer

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

Answer

for item in mylist: print(item.upper)

Question 3

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. Option D is correct because 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 4

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

Accepted Answer

nums[-1]. Option B is correct because 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 5

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 type(item) == str]. Option C is correct because `type(item) == str` directly compares the type of each item to the `str` type object, which returns `True` for strings and `False` for numbers. This is a valid and explicit way to filter the list comprehension to only include string elements.

Answer

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

Answer

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

Question 6

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 7

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

True in flags. Option A is correct because the `in` operator checks membership in a list; `True in flags` returns `True` if at least one element in the list `flags` is the boolean `True`. Option D is also correct because the built-in `any()` function returns `True` if any element in the iterable is truthy, which for a list of booleans means at least one `True`.

Answer

all(flags)

Answer

flags.any()

Question 8

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

Accepted Answer

[1, 2, 3, 4]. Option C is correct because 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 9

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]. Option A is correct because 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 10

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 break statement exits the loop immediately. Therefore, when i becomes 3, the loop terminates before printing 3, so the output is '0 1 2' (each on a new line due to print(i) default behavior). Option C correctly lists the printed values as 0, 1, 2, and then 4 is not printed because the loop breaks before reaching 4.

Answer

No output

Answer

0 1 2 3 4

Answer

0 1 2 4 5

Question 11

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. Option D is correct because 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 12

Which TWO 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)]. Option A is correct because it uses a list comprehension that iterates over the tuple (10, 20, 30) and creates a new list with the same elements. This is a valid Python syntax for constructing a list from an iterable.

Answer

my_list = list(10, 20, 30)

Answer

my_list = [10; 20; 30]

Question 13

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). Option A is correct because `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 14

Which THREE of the following are valid list operations?

Accepted Answer

my_list.extend([5,6]). Option B is correct because 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 15

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']. Option D is correct because 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 16

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]]]. Option D is correct because 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 17

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

Question 18

Arrange the steps to install a third-party Python package using pip.

Question 19

Match each exception type to its description.

Question 20

Match each Python concept to its description.