Python output prediction: practice questions with answers.

What this topic tests

• Trace variables line by line instead of pattern-matching the code.
• Notice when a function or method mutates an object in place.
• Check spaces, newlines, quotes, and print separators before answering.

Common mistakes

• Reading the final expression but ignoring a mutation on an earlier line.
• Assuming print adds a space where sep or end changed the output.
• Answering with the value you expected rather than the characters Python actually writes.

Ten representative questions from the full bank. Try each one before opening the answer.

1. Output predictionq0002

   1. Ming writes the line below. What will it print?

   print(f"Milk tea {3+5} yuan")

   Show answer

   Answer

   Milk tea 8 yuan

   Why: The braces hold an expression rather than text: Python evaluates 3+5 to 8 before formatting, so the label reads Milk tea 8 yuan.

2. Output predictionq0182

   2. What does `decode('zmlyhgzxovrhlugvmzhgvkkrmthglmv')` return?

   from string import ascii_lowercase
   
   
   BLOCK_SIZE = 5
   trtbl = str.maketrans(ascii_lowercase, ascii_lowercase[::-1])
   
   
   def base_trans(text):
       return ''.join([character for character in text if character.isalnum()]).lower().translate(trtbl)
   
   
   def encode(plain):
       cipher = base_trans(plain)
       return ' '.join(cipher[idx:idx + BLOCK_SIZE]
                        for idx in range(0, len(cipher), BLOCK_SIZE))
   
   
   def decode(ciphered):
       return base_trans(ciphered)
   
   print(decode('zmlyhgzxovrhlugvmzhgvkkrmthglmv'))

   Show answer

   Answer

   anobstacleisoftenasteppingstone

   Why: With no spaces the whole run is one block. Each letter is mirrored and the 33 characters spell an obstacle is often a stepping stone.

3. Output predictionq0359

   3. What is the total price of the three coffees?

   prices = [18, 22, 15]
   total = 0
   for price in prices:
       total += price
   print(total)

   Show answer

   Answer

   55

   Why: The loop adds 18, 22 and 15 into total, and print shows 55; total must start at 0 or the first += would raise NameError. Accumulation is the whole pattern.

4. Output predictionq0573

   4. What is the largest element of the set?

   s = {3, 1, 2}
   print(max(s))

   Show answer

   Answer

   3

   Why: max scans the set and returns the largest value, which is 3. Order does not matter because max compares values, not positions.

5. Output predictionq0764

   5. What does `rebase(10, [5], 2)` return?

   def from_digits(digits, base):
       return sum(number * base ** idx for idx, number in enumerate(reversed(digits)))
   
   
   def to_digits(number, base_to):
       result = []
       while number > 0:
           result.append(number % base_to)
           number //= base_to
       if result:
           return result[::-1]  # list(reversed(result))
       return [0]
   
   
   def rebase(from_base, digits, to_base):
       if from_base < 2:
           raise ValueError("input base must be >= 2")
   
       if to_base < 2:
           raise ValueError("output base must be >= 2")
   
       if any(True for idx in digits if idx < 0 or idx >= from_base):
           raise ValueError("all digits must satisfy 0 <= d < input base")
   
       return to_digits(from_digits(digits, from_base), to_base)
   
   print(rebase(10, [5], 2))

   Show answer

   Answer

   [1, 0, 1]

   Why: 5 in base 2 is 4 + 1, so the digits from the highest power down are 1, 0, 1. The function keeps dividing and collecting remainders.

6. Output predictionq1143

   6. The subclass overrides the member total method. What is printed?

   class Order:
       def __init__(self, price):
           self.price = price
       def total(self):
           return self.price
   class MemberOrder(Order):
       def total(self):
           return round(self.price * 0.9, 2)
   print(MemberOrder(18).total())

   Show answer

   Answer

   16.2

   Why: The override multiplies the stored price by 0.9 and rounds to two decimals: 18 × 0.9 = 16.2, so the member price replaces the base one.

7. Output predictionq1448

   7. Revenue descending, name ascending. What is printed?

   rows = [('Hubin', 1800, 'B'), ('Hubin', 1500, 'A'), ('Gaoxin', 1800, 'C')]
   print(sorted(rows, key=lambda r: (-r[1], r[0])))

   Show answer

   Answer

   [('Gaoxin', 1800, 'C'), ('Hubin', 1800, 'B'), ('Hubin', 1500, 'A')]

   Why: -1800 sorts before -1500, so the two 1800 rows come first, and the name decides between them because Gaoxin precedes Hubin.

8. Output predictionq1596

   8. Count occurrences of “latte”. What is printed?

   print('latte latte americano'.count('latte'))

   Show answer

   Answer

   2

   Why: count reports non-overlapping occurrences, so the word 'latte' appears twice in that sentence. count is case-sensitive, so 'Latte' would not be included in those two.

9. Output predictionq1782

   9. The walrus operator assigns and then compares. What is printed?

   if (n := 5) > 3:
       print(n)

   Show answer

   Answer

   5

   Why: The walrus assigns 5 to n inside the condition and hands back that value, so 5 > 3 is true and n is already bound when the body prints it.

10. Output predictionq2320

    10. Deduplicate headlines while preserving order. What is printed?

    titles = ['New arrival', 'Member day', 'New arrival', 'Ranking']
    seen = []
    for title in titles:
        if title not in seen:
            seen.append(title)
    print('|'.join(seen))

    Show answer

    Answer

    New arrival|Member day|Ranking

    Why: The loop appends a title only when it is not already in seen, so the second 'New arrival' is dropped and the original order survives.

Common questions