【超入門】Pythonの基本文法：変数・型・演算子・条件分岐・ループを一気に攻略（保存版）

# 代入は「名前 = 値」
name = "Taro"
age = 29
pi = 3.14159
is_active = True  # True/False は大文字

# 型を確認
print(type(name), type(age), type(pi), type(is_active))

# 数値演算
x = 10
print(x + 3, x - 3, x * 3, x / 3, x // 3, x % 3, x ** 2)

# 文字列の結合と繰り返し
print("Hello" + " " + name)
print("-" * 10)

# list：可変の順序付きコレクション
nums = [10, 20, 30]
nums.append(40)
nums[0] = 11
print(nums, nums[:2], nums[-1])  # スライス/末尾

# tuple：不変（読み取り専用）の並び
point = (3, 5)

# dict：キーと値のペア（最頻出）
user = {"name": "Taro", "age": 29}
user["job"] = "analyst"
print(user.get("age"), user.keys(), user.values())

# set：重複なし集合（会員IDの一意化など）
ids = {101, 102, 102, 103}
print(ids)  # {101, 102, 103}

# よく使うイディオム（内包表記）
squares = [i*i for i in range(5)]  # [0, 1, 4, 9, 16]
evens = [i for i in range(10) if i % 2 == 0]
name_lengths = {n: len(n) for n in ["sato", "suzuki"]}

s = "  Python,Data,Science  "
print(s.strip())               # 前後空白除去
print(s.lower())               # 小文字化
print("python" in s.lower())   # 含有判定
print("|".join(["A", "B", "C"]))  # 結合
print("Taro:{age}".format(age=29))    # format

# f文字列（最推奨）：読みやすく速い
name, age = "Taro", 29
print(f"{name} is {age} years old")

# if / elif / else
score = 72
if score >= 80:
    grade = "A"
elif score >= 65:
    grade = "B"
else:
    grade = "C"
print(grade)

# for ループ
for n in ["sato", "suzuki", "tanaka"]:
    print(n)

# enumerate：インデックスも欲しい
for i, n in enumerate(["sato", "suzuki"]):
    print(i, n)

# range：0..N-1
for i in range(3):
    print(i)

# while：条件が続く限り
c = 3
while c > 0:
    c -= 1

def add(a: int, b: int) -> int:
    """2つの整数を足して返す（型ヒント付き）"""
    return a + b

print(add(2, 3))

# デフォルト引数と可変長
from typing import Iterable, Any

def flatten(items: Iterable[Iterable[Any]]) -> list[Any]:
    out: list[Any] = []
    for it in items:
        out.extend(it)
    return out

print(flatten([[1,2],[3,4]]))

try:
    val = int("42")  # ここで例外が出るかも
except ValueError as e:
    print("数値に変換できません", e)
else:
    print("成功", val)
finally:
    print("後片付け")

from pathlib import Path
p = Path("sample.txt")

# 書き込み
with p.open("w", encoding="utf-8") as f:
    f.write("hello\n")

# 読み込み
with p.open("r", encoding="utf-8") as f:
    content = f.read()
print(content)

# 標準ライブラリ
from datetime import datetime, timedelta
print(datetime.now() + timedelta(days=7))

# 自作モジュール（同ディレクトリの util.py から）
# util.py に def greet(name): return f"Hello {name}" と定義しておく
from util import greet
print(greet("Taro"))

from dataclasses import dataclass

@dataclass
class Config:
    input_path: str = "data/input.csv"
    threshold: float = 0.5

CONFIG = Config()

def main() -> None:
    print(f"Read from {CONFIG.input_path}, threshold={CONFIG.threshold}")

if __name__ == "__main__":
    main()

from pathlib import Path
import csv
from collections import defaultdict

in_path = Path("expenses.csv")
out_path = Path("summary.csv")

def read_rows(path: Path) -> list[dict[str, str]]:
    with path.open("r", encoding="utf-8") as f:
        return list(csv.DictReader(f))

def summarize(rows: list[dict[str, str]]) -> list[dict[str, str]]:
    agg = defaultdict(float)
    for r in rows:
        ym = r["date"][:7]  # YYYY-MM
        key = (ym, r["category"])
        agg[key] += float(r["amount"])
    return [
        {"year_month": k[0], "category": k[1], "amount": f"{v:.0f}"}
        for k, v in sorted(agg.items())
    ]

def write_rows(path: Path, rows: list[dict[str, str]]):
    with path.open("w", encoding="utf-8", newline="") as f:
        w = csv.DictWriter(f, fieldnames=["year_month", "category", "amount"])
        w.writeheader()
        w.writerows(rows)

if __name__ == "__main__":
    try:
        rows = read_rows(in_path)
        summary = summarize(rows)
        write_rows(out_path, summary)
        print(f"Saved: {out_path.resolve()}")
    except Exception as e:
        print(f"Error: {e}")
        raise

# Truthy/Falsy（if判定で False になるもの）
# False, None, 0, 0.0, "", [], {}, set(), range(0)

# 三項演算子（式版の if）
score = 72
status = "OK" if score >= 60 else "NG"

# 辞書の安全取得と初期化
user = {}
value = user.get("key", "default")
user.setdefault("visited", 0)
user["visited"] += 1

# 例外の再送出（ログを残してから）
def risky(): ...
try:
    risky()
except Exception as e:
    print(f"error: {e}")
    raise

# 一時リストを作らずジェネレータで
sum_len = sum(len(s) for s in ["a", "bbb", "cc"])