4~6주차 — 표준 라이브러리 · 예외 처리 · 파일 입출력

from datetime import datetime, date, timedelta

now = datetime.now()
print(now.strftime("%Y-%m-%d %H:%M"))

today = date.today()
print("오늘:", today)
print("일주일 후:", today + timedelta(days=7))

birthday = date(2000, 5, 9)
print(f"태어난 후 {(today - birthday).days}일")

2026-05-10 14:32
오늘: 2026-05-10
일주일 후: 2026-05-17
태어난 후 9498일

import random
random.seed(42)   # 재현 가능

print(random.random())
print(random.randint(1, 100))
print(random.choice(["가위", "바위", "보"]))
print(random.sample(range(1, 46), 6))

xs = [1, 2, 3, 4, 5]
random.shuffle(xs)
print(xs)

0.6394267984578837
82
바위
[8, 14, 21, 27, 36, 41]
[3, 1, 4, 5, 2]

from pathlib import Path

p = Path("data") / "hello.txt"
p.parent.mkdir(parents=True, exist_ok=True)
p.write_text("Hello!", encoding="utf-8")
print(p.read_text(encoding="utf-8"))
print(p.exists(), p.suffix, p.name, p.stem)

# 현재 폴더의 .py 파일 목록
for f in Path(".").glob("*.py"):
    print(f.name)

Hello!
True .txt hello.txt hello
01_datetime.py
02_random.py
03_pathlib.py
04_collections.py

from collections import Counter, defaultdict, deque

text = "to be or not to be that is the question to be"
c = Counter(text.split())
print(c.most_common(3))

groups = defaultdict(list)
for name, age in [("A", 20), ("B", 25), ("C", 20)]:
    groups[age].append(name)
print(dict(groups))

dq = deque([1, 2, 3])
dq.appendleft(0)
dq.append(4)
print(dq)

[('to', 3), ('be', 3), ('or', 1)]
{20: ['A', 'C'], 25: ['B']}
deque([0, 1, 2, 3, 4])

try:
    n = int(input("숫자: "))
    print(10 / n)
except ValueError:
    print("숫자가 아닙니다")
except ZeroDivisionError:
    print("0으로 나눌 수 없습니다")
except Exception as e:
    print(f"기타 에러: {e}")

숫자: abc
숫자가 아닙니다

숫자: 0
0으로 나눌 수 없습니다

숫자: 5
2.0

try:
    f = open("hello.txt", encoding="utf-8")
except FileNotFoundError:
    print("파일 없음")
else:
    print(f.read())
    f.close()
finally:
    print("정리 완료")

# 파일 있을 때
Hello, World!
정리 완료

# 파일 없을 때
파일 없음
정리 완료

def withdraw(balance, amount):
    if amount <= 0:
        raise ValueError("금액은 양수여야 합니다")
    if amount > balance:
        raise ValueError("잔액 부족")
    return balance - amount

try:
    print(withdraw(1000, 500))
    print(withdraw(500, 1000))
except ValueError as e:
    print("에러:", e)

500
에러: 잔액 부족

class InsufficientFundsError(Exception):
    pass

class Account:
    def __init__(self, balance):
        self.balance = balance

    def withdraw(self, amount):
        if amount > self.balance:
            raise InsufficientFundsError(
                f"잔액 {self.balance} < 요청 {amount}"
            )
        self.balance -= amount

try:
    a = Account(1000)
    a.withdraw(2000)
except InsufficientFundsError as e:
    print("거래 거부:", e)

거래 거부: 잔액 1000 < 요청 2000

# 쓰기
with open("notes.txt", "w", encoding="utf-8") as f:
    f.write("첫 줄\n")
    f.writelines(["A\n", "B\n", "C\n"])

# 읽기 (한 줄씩)
with open("notes.txt", encoding="utf-8") as f:
    for line in f:
        print(line.rstrip())

첫 줄
A
B
C

import csv

with open("scores.csv", "w", encoding="utf-8", newline="") as f:
    w = csv.writer(f)
    w.writerow(["name", "score"])
    w.writerows([
        ["Alice", 92],
        ["Bob", 78],
        ["Charlie", 88],
    ])

print("저장 완료")

저장 완료

# scores.csv 내용:
name,score
Alice,92
Bob,78
Charlie,88

import csv

with open("scores.csv", encoding="utf-8") as f:
    for row in csv.DictReader(f):
        name = row["name"]
        score = int(row["score"])
        print(f"{name}: {score}")

Alice: 92
Bob: 78
Charlie: 88

import json

data = {
    "name": "홍길동",
    "skills": ["Python", "SQL"],
    "active": True,
}

with open("profile.json", "w", encoding="utf-8") as f:
    json.dump(data, f, ensure_ascii=False, indent=2)

with open("profile.json", encoding="utf-8") as f:
    loaded = json.load(f)

print(loaded["name"])
print(loaded["skills"])

홍길동
['Python', 'SQL']