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Reverse Quiz: Streaming vs Loading

Question 1

Read the code.

numbers = [1, 2, 3]
it = iter(numbers)

print(next(it))
print(next(it))

Which output does this code produce?

Options:

  • 1 then 1
  • 1 then 2
  • 2 then 3
  • StopIteration immediately

Answer: 2 Type: single Time: 45 Explanation: The iterator remembers its position, so the first next(it) gives 1 and the second gives 2.

Question 2

Read the code.

with open("les_miserables.txt", "r", encoding="utf-8") as file:
    lines = file.readlines()

print(lines[100])

Which description best matches this code?

Options:

  • It reads only one line from disk
  • It is the best choice when the file is too large for memory
  • It streams the file one character at a time
  • It loads all lines before using an index

Answer: 4 Type: single Time: 45 Explanation: readlines() stores all lines in a list, which then allows indexing with lines[100].

Question 3

Read the code.

found = None

with open("les_miserables.txt", "r", encoding="utf-8") as file:
    for line in file:
        if "Jean Valjean" in line:
            found = line
            break

print(found)

What is the main benefit of break here?

Options:

  • It stops reading after the first match is found
  • It loads all matching lines into memory
  • It sorts the file before searching
  • It prevents the file from opening

Answer: 1 Type: single Time: 45 Explanation: Once the first matching line is found, break stops the loop so the rest of the file does not need to be read.

Question 4

Read both snippets.

# A
count = 0
with open("les_miserables.txt", "r", encoding="utf-8") as file:
    for line in file:
        count += 1
print(count)
# B
total_length = 0
count = 0
with open("les_miserables.txt", "r", encoding="utf-8") as file:
    for line in file:
        total_length += len(line)
        count += 1
print(total_length / count)

Which statement is correct?

Options:

  • A streams, but B must load all lines
  • B streams, but A must load all lines
  • Both process one line at a time without storing the whole file
  • Neither uses a file iterator

Answer: 3 Type: single Time: 50 Explanation: Both snippets loop over the file directly and keep only small variables such as counters and totals.

Question 5

Read the code.

def non_empty_lines(path):
    with open(path, "r", encoding="utf-8") as file:
        for line in file:
            line = line.strip()
            if line != "":
                yield line

for line in non_empty_lines("les_miserables.txt"):
    print(line)
    break

Which description best matches this code?

Options:

  • yield returns the whole file as one final value
  • The generator produces non-empty lines one at a time
  • break makes the generator load all remaining lines
  • strip() sorts the lines alphabetically

Answer: 2 Type: single Time: 50 Explanation: The generator uses yield to produce one non-empty line at a time, and the loop stops after printing the first one.