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Convert two loops to comprehensions on Python 3.7

Practice: Setting limits and rules. About 5 minutes.

About this exercise

Convert the loops in active_emails and price_map to comprehensions. The lab server runs Python 3.7, so no walrus operator (:=). active_emails must keep order and duplicates (the attendance report counts them). price_map still skips blank prices, and the club treasurer now wants each price rounded to 2 decimals. Keep both docstrings word for word, make each body a single return statement, and leave load_rows alone. Return only the two functions in exactly 1 code block of at most 10 lines, under 20 words of text.

Common mistakes when you ask AI for this

  • Using the walrus operator. To avoid stripping twice, the AI reaches for :=, which crashes on Python 3.7. Try: Add: "Python 3.7: no walrus operator."
  • Deduping by accident. A set comprehension looks tidy but drops the duplicates the attendance report needs. Try: Add: "Keep order and duplicates: a list, not a set."
  • Missing the rounding. The AI only converts what's there; it can't know the treasurer wants 2 decimals. Try: Add: "round(float(row['price']), 2); still skip blank prices."
  • Rewriting the module. The AI reprints the file, drops docstrings or refactors load_rows too. Try: Add: "Only these two functions, docstrings unchanged, one return each."

What a strong prompt includes

  • Names the Python version
  • Keeps duplicates
  • Adds the rounding
  • Protects the docstrings
  • Asks for only two functions

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