csvEx2.py

# CSV 쓰기

import csv

subjects = ['국어', '영어', '수학']

# 먼저 읽어서 집계
with open('data/scores.csv', 'r', encoding='utf-8') as f:
    students = list(csv.DictReader(f))

rows = []
for s in students:
    scores = [int(s[sub]) for sub in subjects]
    rows.append({
        '이름': s['이름'],
        '학년': int(s['학년']),
        '총점': sum(scores),
        '평균': round(sum(scores) / len(scores), 2),
    })

print('---------- writer : 리스트를 쓴다 ----------')
# newline='' 을 꼭 주세요. 없으면 윈도우에서 빈 줄이 하나씩 끼어듭니다.
with open('output/summary1.csv', 'w', encoding='utf-8', newline='') as f:
    writer = csv.writer(f)
    writer.writerow(['이름', '학년', '총점', '평균'])       # 헤더
    for r in rows:
        writer.writerow([r['이름'], r['학년'], r['총점'], r['평균']])
print('summary1.csv 작성 완료')

print('---------- DictWriter : 딕셔너리를 쓴다 ----------')
with open('output/summary2.csv', 'w', encoding='utf-8', newline='') as f:
    writer = csv.DictWriter(f, fieldnames=['이름', '학년', '총점', '평균'])
    writer.writeheader()
    writer.writerows(rows)                                  # 한 번에
print('summary2.csv 작성 완료')

print('---------- 결과 확인 ----------')
with open('output/summary2.csv', 'r', encoding='utf-8') as f:
    print(f.read())

print('---------- 평균 상위 3명만 따로 ----------')
top3 = sorted(rows, key=lambda r: r['평균'], reverse=True)[:3]
with open('output/top3.csv', 'w', encoding='utf-8', newline='') as f:
    writer = csv.DictWriter(f, fieldnames=['이름', '학년', '총점', '평균'])
    writer.writeheader()
    writer.writerows(top3)

for r in top3:
    print(f"{r['이름']} {r['평균']}")