PCEP Control Flow, Loops, Lists and Logic — 10 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?

Choose an answer to begin — your selection is scored in the full session.

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 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()). 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 3

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 4

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 5

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 6

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 7

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 8

Match each exception type to its description.

Accepted Answer

ValueError: Raised when a function gets an argument with correct type but inappropriate value. These are built-in exceptions in Python that indicate specific error conditions.

Answer

ValueError: Raised when an operation or function is applied to an object of inappropriate type

Answer

IndexError: Raised when a dictionary key is not found

Question 9

Match each Python concept to its description.

Accepted Answer

Module: A file containing Python definitions and statements. The correct matches are: Module is a single file; Package is a directory of modules; Class is a blueprint; Function is reusable code. Common mistakes are confusing module and package definitions.

Answer

Module: A collection of modules organized in a directory tree

Answer

Package: A file containing Python definitions and statements

Question 10

A junior developer needs to write code that processes a list of student scores and stops processing when a score of 100 is encountered, as that score represents a perfect score that should be treated separately. Which loop construct is most appropriate?

Accepted Answer

for score in scores: if score == 100: break ... further processing. The `break` statement immediately exits the loop when a score of 100 is encountered, which matches the requirement to stop processing further scores. The `for` loop iterates over the list naturally, and the `if` condition checks for the perfect score, making this the most straightforward and efficient construct for this scenario.

Answer

for score in scores: if score == 100: pass ...

Answer

for i in range(len(scores)): if scores[i] == 100: exit() ...

Answer

while scores: score = scores.pop(); if score == 100: continue ...