コレクションと内包表記

nums: list[int] = [1, 2, 3]

nums.append(4)         # [1, 2, 3, 4]
nums.insert(0, 0)      # [0, 1, 2, 3, 4]
nums.remove(2)         # [0, 1, 3, 4]
last = nums.pop()      # 4 を返し、リストは [0, 1, 3]

print(len(nums))       # 3
print(nums[0])         # 0
print(3 in nums)       # True

items = [10, 20, 30, 40, 50]

items[1:3]    # [20, 30]    1 以上 3 未満
items[:2]     # [10, 20]    先頭から 2 未満
items[3:]     # [40, 50]    3 以上から末尾まで
items[-2:]    # [40, 50]    末尾から 2 個
items[::2]    # [10, 30, 50]  step 2
items[::-1]   # [50, 40, 30, 20, 10]   反転

[1, 2] + [3, 4]   # [1, 2, 3, 4]
[0] * 5           # [0, 0, 0, 0, 0]

matrix = [[]] * 3
matrix[0].append(1)
print(matrix)
# [[1], [1], [1]]   ← すべて同じリストを指している!

point: tuple[float, float] = (1.0, 2.0)
person: tuple[str, int] = ("カーティス", 30)

# tuple は通常 unpack して使う
name, age = person
print(name, age)   # カーティス 30

# 一要素 tuple はカンマ必須 — 括弧だけでは不足
single = (42,)     # tuple
not_tuple = (42)   # ただの整数

from typing import NamedTuple

class Person(NamedTuple):
    name: str
    age: int

p = Person("カーティス", 30)
print(p.name, p.age)   # カーティス 30

# tuple のように unpack も可
name, age = p

user: dict[str, int] = {"id": 1, "age": 30}

print(user["id"])              # 1
print(user.get("nope"))        # None  (ないキー → 安全)
print(user.get("nope", -1))    # -1    (デフォルト値)

user["name"] = "curtis"        # 追加/更新
del user["age"]                # 削除
print("name" in user)          # True

for key in user:                # キーだけ
    print(key)

for key, value in user.items(): # 両方
    print(key, value)

for value in user.values():     # 値だけ
    print(value)

defaults = {"a": 1, "b": 2}
overrides = {"b": 20, "c": 30}

merged = defaults | overrides
print(merged)    # {"a": 1, "b": 20, "c": 30}

unique: set[int] = {1, 2, 3, 2, 1}
print(unique)   # {1, 2, 3}

unique.add(4)      # {1, 2, 3, 4}
unique.discard(2)  # {1, 3, 4}
print(3 in unique) # True

# 空 set は set() — {} は空 dict
empty = set()

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}

a | b   # 和集合  {1, 2, 3, 4, 5, 6}
a & b   # 積集合  {3, 4}
a - b   # 差集合  {1, 2}
a ^ b   # 対称差  {1, 2, 5, 6}

items = [1, 2, 1, 3, 2, 4]
unique = list(dict.fromkeys(items))
print(unique)   # [1, 2, 3, 4]

# [式 for 変数 in イテラブル]

squares = [x ** 2 for x in range(5)]
# [0, 1, 4, 9, 16]

squares = []
for x in range(5):
    squares.append(x ** 2)

evens = [x for x in range(10) if x % 2 == 0]
# [0, 2, 4, 6, 8]

# 偶数だけ選んで二乗
result = [x ** 2 for x in range(10) if x % 2 == 0]
# [0, 4, 16, 36, 64]

labels = ["even" if x % 2 == 0 else "odd" for x in range(5)]
# ['even', 'odd', 'even', 'odd', 'even']

matrix = [[0 for _ in range(3)] for _ in range(3)]
# [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

square_map = {x: x ** 2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

# キー-値 swap
user = {"id": 1, "name": "curtis"}
swapped = {v: k for k, v in user.items()}
# {1: "id", "curtis": "name"}

unique_lengths = {len(w) for w in ["a", "bb", "cc", "ddd"]}
# {1, 2, 3}

pairs = [(x, y) for x in [1, 2] for y in ['a', 'b']]
# [(1, 'a'), (1, 'b'), (2, 'a'), (2, 'b')]

pairs = []
for x in [1, 2]:
    for y in ['a', 'b']:
        pairs.append((x, y))

gen = (x ** 2 for x in range(1_000_000))
print(gen)   # <generator object ...>

total = sum(x ** 2 for x in range(1_000_000))
# 関数に直接入れるときは () を省略できる

# 一行で可能だが読みにくい
result = [transform(x) for x in items if validate(x) and is_active(x) and not is_deleted(x)]

# ばらして書くとデバッグもしやすく読みやすい
result = []
for x in items:
    if not validate(x):
        continue
    if not is_active(x) or is_deleted(x):
        continue
    result.append(transform(x))