回答編集履歴
2
修正
answer
CHANGED
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@@ -7,37 +7,46 @@
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実際にidを確認してみると良いです。
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```Python
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a = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
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10
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a[1][1] = 1
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for e in a:
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print(id(e))
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print(f'{id(e)}: {e}')
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print()
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print('-'*42)
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16
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#
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#
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b = [[0] * 3] * 3
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b[1][1] = 1
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for e in b:
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print(id(e))
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print(f'{id(e)}: {e}')
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print()
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print('-'*42)
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#
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#
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c = [[0] * 3 for _ in range(3)]
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c[1][1] = 1
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for e in c:
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print(id(e))
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print(f'{id(e)}: {e}')
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print('-'*42)
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36
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```
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37
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-
**実行結果** [Wandbox](https://wandbox.org/permlink/
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38
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+
**実行結果** [Wandbox](https://wandbox.org/permlink/HEZpkk81o8qx6UYW)
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39
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```
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-
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139895659521672: [0, 0, 0]
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139752138114888
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-
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139895659521864: [0, 1, 0]
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-
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139752138115336
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139752138115336
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-
139752138115336
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-
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139752138116296
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-
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139895659522184: [0, 0, 0]
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------------------------------------------
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-
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139895659523656: [0, 1, 0]
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139895659523656: [0, 1, 0]
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139895659523656: [0, 1, 0]
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------------------------------------------
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139895659523976: [0, 0, 0]
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139895659524040: [0, 1, 0]
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139895659544648: [0, 0, 0]
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------------------------------------------
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43
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```
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1
追記
answer
CHANGED
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@@ -1,4 +1,43 @@
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1
1
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後者は、リストの参照値が共有されてしまうからです。
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2
2
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[Qiita - pythonでのリストの要素の変更とリストのコピー](https://qiita.com/masarin1126/items/a0afa4a5fecacdd02be9)
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3
3
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4
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-
良く躓くポイントなので、調べれば同様の話題はたくさん出てきます。
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4
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良く躓くポイントなので、調べれば同様の話題はたくさん出てきます。
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5
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+
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6
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+
---
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7
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+
実際にidを確認してみると良いです。
|
|
8
|
+
```Python
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|
9
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+
a = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
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10
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+
for e in a:
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11
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print(id(e))
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12
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13
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print()
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14
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15
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#
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16
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#
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17
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b = [[0] * 3] * 3
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18
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for e in b:
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print(id(e))
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20
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print()
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22
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23
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#
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24
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#
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25
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c = [[0] * 3 for _ in range(3)]
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26
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for e in c:
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27
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print(id(e))
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28
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```
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29
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+
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30
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+
**実行結果** [Wandbox](https://wandbox.org/permlink/xdcNb06JtTjRN3AI)
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```
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32
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139752138114696
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139752138114888
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139752138115208
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139752138115336
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139752138115336
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139752138115336
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139752138116296
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139752138116360
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42
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139752138116424
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43
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```
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