Trivia: Mary Badham was nominated for the Best Supporting Actress Academy Award for her role as Scout. At the age of nine, Badham became the youngest ever nominee in that category.
Trivia: Gregory Peck won his only Oscar for his role as Atticus Finch in this movie.
Answer: The film is set in Maycomb, Georgia. There's no explanation, so any answer is speculation. However, Atticus usually wore a three-piece suit, so it was a vest, not a sweater. The suit was likely a lightweight material and was a typical style of the era. Atticus probably considered it a more professional look for a lawyer. Most likely this was a movie wardrobe decision, giving Atticus a scholarly appearance and persona throughout the film, even if in reality, it wasn't practical.
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