【Python】enumerateの使い方｜実務で使う場面とREST API例

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enumerate(iterable, start=0)

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lst = ["A", "B", "C"]

e = enumerate(lst)

print(list(e))
# [(0, 'A'), (1, 'B'), (2, 'C')]

print(list(e))
# []  ← イテレータなので一度消費すると空になる

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lst = ["A", "B", "C"]

for index, value in enumerate(lst):
    print(index, value)

# 0 A
# 1 B
# 2 C

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lst = ["A", "B", "C"]

it = enumerate(lst)

while True:
    try:
        index, value = next(it)
        print(index, value)
    except StopIteration:
        break

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lst = ["A", "B", "C"]    

print([index for index, value in enumerate(lst)])
# [0, 1, 2] 

print([value for index, value in enumerate(lst)])
# ['A', 'B', 'C']

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lst = ["A", "B", "C"]    

print({index: value for index, value in enumerate(lst)})
# {0: 'A', 1: 'B', 2: 'C'}

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lst = ["A", "B", "C"]    

print({value for index, value in enumerate(lst)})
# {'A', 'B', 'C'}

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users = [
    {"id": "u1", "name": "mori"},
    {"id": "u2", "name": "shimada"},
]

# 表示用に連番(no)を付与（1始まり）
view_models = [
    {"no": i, **user}
    for i, user in enumerate(users, start=1)
]

# [{'no': 1, 'id': 'u1', 'name': 'mori'}, {'no': 2, 'id': 'u2', 'name': 'shimada'}]

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from pydantic import BaseModel, ValidationError, Field

class UserIn(BaseModel):
    user_id: int
    name: str
    age: int = Field(ge=0)  # 0以上

payload = [
    {"user_id": 1, "name": "mori", "age": 20},
    {"user_id": "x", "name": "shimada", "age": 50},
    {"user_id": 3, "name": "kyogoku", "age": -1},
]

errors = []
valid = []

for row, data in enumerate(payload, start=1):
    try:
        valid.append(UserIn.model_validate(data))
    except ValidationError as e:
        errors.append({"row": row, "errors": e.errors()})