{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"<p style=\"text-align:center\">\n",
" <a href=\"https://nbviewer.jupyter.org/github/twMr7/Python-Machine-Learning/blob/master/06-Tuple_Operations.ipynb\">\n",
" Open In Jupyter nbviewer\n",
" <img style=\"float: center;\" src=\"https://nbviewer.jupyter.org/static/img/nav_logo.svg\" width=\"120\" />\n",
" </a>\n",
"</p>"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"[](https://colab.research.google.com/github/twMr7/Python-Machine-Learning/blob/master/06-Tuple_Operations.ipynb)\n",
"\n",
"# 6. `tuple` 序列容器操作\n",
"\n",
"`tuple` 也是存放序列性資料的結構。語法使用逗號 `,` 分隔資料元素，用小括號（parentheses）`(` `)` 成對包住所有元素，但括號可以省略。 `tuple` 可以是巢狀多維度的，同一個 `tuple` 中也可以存放異質類型資料，通常使用在函式參數的傳遞與回傳。\n",
"\n",
"元素內容是按照儲存順序的 index 存取，語法為 **`[ index ]`**。 如果按照由前往後的順序，**第一個元素 index 是0**，依次往後遞增； 如果反過來由後往前存取，**最後一個元素 index 可以用-1**，依次向前遞減。\n",
"\n",
"| Tuple 範例 | 說明 |\n",
"|------------------------------------|-----------------------------------------------|\n",
"| `()` | 空的 tuple |\n",
"| `('code',)` | 單一元素的 tuple |\n",
"| `(5, 6, 7, 8)` | 四個數字元素的 tuple |\n",
"| `('code', (42, 3.1415), 1.23, {})` | 巢狀、異質的 tuple |\n",
"| `'code', 42, 3.1415, 1.23` | 括號可以省略 |\n",
"\n",
"- 內建函式 `tuple()` 可以用來建構一個新的tuple。\n",
"- 內建函式 `len()` 可以用來回傳容器裡的元素個數。\n",
"- 內建函式 `min()` 可以用來回傳容器中最小的元素。\n",
"- 內建函式 `max()` 可以用來回傳容器中最大的元素。\n",
"\n",
"`tuple` 在建立後，元素內容**不可以**就地變更（immutable）。 `tuple` 是序列容器，所以一般 immutable 序列容器的共同方法都可以用，參閱官方文件 [Common Sequence Operations](https://docs.python.org/3/library/stdtypes.html#common-sequence-operations)。\n"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § `tuple` 是不能 In-Place 就地變更的序列容器。"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"T = (123, '345', (5, 67), 7.89).\n"
]
}
],
"source": [
"T = 123, '345', (5, 67), 7.89\n",
"print('T = {}.'.format(T))"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"the last element is 7.89\n"
]
}
],
"source": [
"# 可以用索引讀取，但想要變更元素值一定會出現 TypeError\n",
"#T[-1] = 987\n",
"print('the last element is {}'.format(T[-1]))"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"T = ([123], ['345'], [5, 67], [7.89]).\n"
]
}
],
"source": [
"# 但 tuple 裡面可以放 mutable 的物件\n",
"T = [123], ['345'], [5, 67], [7.89]\n",
"print('T = {}.'.format(T))"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"the last element is now [987]\n"
]
}
],
"source": [
"# tuple 裡的 mutable 物件內容當然可以 in-place 修改\n",
"T[-1][0] = 987\n",
"print('the last element is now {}'.format(T[-1]))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 一般序列容器的串接、重複複製、和 slicing 都可以用"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"T = ([123], ['345'], [5, 67], [987], [6, 54], ['32']).\n"
]
}
],
"source": [
"# 串接\n",
"T += [6, 54], ['32']\n",
"print('T = {}.'.format(T))"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"T = ([123], ['345'], [5, 67], [123], ['345'], [5, 67], [123], ['345'], [5, 67]).\n"
]
}
],
"source": [
"# 重複複製\n",
"T = T[:3] * 3\n",
"print('T = {}.'.format(T))"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [
{
"ename": "TypeError",
"evalue": "'tuple' object does not support item assignment",
"output_type": "error",
"traceback": [
"\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)",
"\u001b[1;32m<ipython-input-7-12b6efc4295e>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m 1\u001b[0m \u001b[1;31m# tuple 的成員不能 in-place 修改，\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[0mT\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m2\u001b[0m\u001b[1;33m]\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'X'\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[1;31mTypeError\u001b[0m: 'tuple' object does not support item assignment"
]
}
],
"source": [
"# tuple 的成員不能 in-place 修改，\n",
"T[2] = 'X'"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"T = ([123], ['345'], ['X', 67], [123], ['345'], ['X', 67], [123], ['345'], ['X', 67]).\n"
]
}
],
"source": [
"# 但元素是 mutable 的其元素可以 in-place 修改\n",
"T[2][0] = 'X'\n",
"print('T = {}.'.format(T))"
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"T = (['345'], ['X', 67], [123]).\n"
]
}
],
"source": [
"# slicing 指定從原本的片段中產生新的 list 物件\n",
"T = T[1:4]\n",
"print('T = {}.'.format(T))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 序列容器的元素卸載 (unpacking)"
]
},
{
"cell_type": "code",
"execution_count": 10,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"a = ['345'], b = ['X', 67], c = [123].\n"
]
}
],
"source": [
"# 卸載常見於函式的回傳值\n",
"a, b, c = T\n",
"print('a = {}, b = {}, c = {}.'.format(a, b, c))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 為甚麼要有 `tuple` 這樣的容器\n",
"有 `list` 這麼方便好用的容器了，為甚麼還需要 `tuple` 這種限制多、操作方法少的容器？\n",
"- `tuple` 不能就地變更 (immutability) 的特性，對於維護程式中資料的完整性 (integrity) 是有幫助的。\n",
"- Immutability 及 integrity 是維持物件關聯性記錄的重要特性，也就是這樣的特性，`dict` 容器的 key 可以是 `tuple` 但不能用 `list`。"
]
}
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