{
"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/07-Dict_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/07-Dict_Operations.ipynb)\n",
"\n",
"# 7. `dict` 容器操作\n",
"\n",
"`dict` 是非序列式的資料結構，元素內容的儲存是成對的 key 和對應的 value。語法使用冒號組成 key 和 value 對應組 `key:value`，以逗號 `,` 分隔對應組元素，用大括號（curly braces）`{` `}` 成對包住所有元素。 同一個 `dict` 中的 `value` 可以存放異質類型資料。 `dict` 也可以是巢狀的，也就是 `value` 中含有另外一個 `dict` 類型的資料。\n",
"\n",
"元素內容必須用 `key` 來存取，語法為 **`[ key ]`**。\n",
"\n",
"| Dict 範例 | 說明 |\n",
"|------------------------------------|-----------------------------------------------|\n",
"| `{}` | 空的 dict |\n",
"| `{'alpha': 2, 'beta': 3}` | 兩個元素的 dict |\n",
"| `{ 'parameter': { 42: 1.5, 'angle': 30 }, 'date': ['2018-06-08'] }` | 巢狀、異質的 dict |\n",
"| `dict([['a', 1], ['b', 2], ['c', 3]])` | 由list中建構一個新的dict物件 |\n",
"\n",
"- 內建函式 `dict()` 可以用來從現有物件的資料實體中生成一個新的tuple。\n",
"- 內建函式 `len()` 可以用來回傳容器裡key-value對的個數。\n",
"\n",
"`dict` 在建立後，元素的 `value` **可以**就地變更（mutable），`key` 不可以就地變更（immutable），也不允許 mutable 的物件類型當 `key`。 `dict` 提供的方法，請參閱官方文件 [4.10 Mapping Types — dict](https://docs.python.org/3/library/stdtypes.html#mapping-types-dict)：\n",
"- `clear()` 清除所有容器內的內容。\n",
"- `copy()` 複製。\n",
"- `get()` 回傳某個 key 的對應 value，沒有的話就回傳預設值。\n",
"- `pop()` 回傳並移除某個 key 的對應 value，沒有的話就回傳預設值。\n",
"- `items()` 回傳可迭代的所有 (key, value) view。\n",
"- `keys()` 回傳可迭代的所有 key 的 view。\n",
"- `values()` 回傳可迭代的所有 value 的 view。\n"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § `dict` 成員的基本操作"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"extno = {'Adam': 3030, 'Brown': 2543}\n"
]
}
],
"source": [
"extno = { 'Adam': 3030, 'Brown': 2543}\n",
"print('extno = {}'.format(extno))"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [
{
"ename": "KeyError",
"evalue": "'Cathy'",
"output_type": "error",
"traceback": [
"\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[1;31mKeyError\u001b[0m Traceback (most recent call last)",
"\u001b[1;32m<ipython-input-2-70ab3a4166b7>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m 1\u001b[0m \u001b[1;31m# 讀取一個不存在的 key 會出現 KeyError 的錯誤\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[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mextno\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;34m'Cathy'\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[1;31mKeyError\u001b[0m: 'Cathy'"
]
}
],
"source": [
"# 讀取一個不存在的 key 會出現 KeyError 的錯誤\n",
"print(extno['Cathy'])"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"extno = {'Adam': 3030, 'Brown': 2543, 'Cathy': 1234}, 3個成員\n"
]
}
],
"source": [
"# 指定一個沒有的 key 就會新增\n",
"extno['Cathy'] = 1234\n",
"print('extno = {}, {}個成員'.format(extno, len(extno)))"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Brown's extension number = 2567\n"
]
}
],
"source": [
"# 修改對應值\n",
"extno['Brown'] = 2567\n",
"print(\"Brown's extension number = {}\".format(extno['Brown']))"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"\n",
"after delete Adam, extno = {'Brown': 2567, 'Cathy': 1234}, 2個成員\n"
]
}
],
"source": [
"# 刪除\n",
"del extno['Adam']\n",
"print('\\nafter delete Adam, extno = {}, {}個成員'.format(extno, len(extno)))"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Is Adam in the ext record? (False)\n"
]
}
],
"source": [
"# 檢查成員是否存在某個 key\n",
"print('Is Adam in the ext record? ({})'.format('Adam' in extno))"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Add Adam back, Adam's extension number is now = 3080\n",
"extno = {'Brown': 2567, 'Cathy': 1234, 'Adam': 3080}\n"
]
}
],
"source": [
"# 把 Adam 加回去\n",
"extno['Adam'] = 3080\n",
"print(\"Add Adam back, Adam's extension number is now = {}\".format(extno['Adam']))\n",
"print('extno = {}'.format(extno))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § `dict` 成員的 Views"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"dict_items([('Brown', 2567), ('Cathy', 1234), ('Adam', 3080)])\n"
]
}
],
"source": [
"# items() 的方法回傳一個 dict_items 的 view 物件，包含所有成員的成對的 key-value\n",
"print(extno.items())\n",
"# 把 view 卸載\n",
"item_list = list(extno.items())"
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"dict_keys(['Brown', 'Cathy', 'Adam'])\n"
]
}
],
"source": [
"# keys() 的方法回傳一個 dict_keys 的 view 物件，包含所有成員的 key\n",
"print(extno.keys())\n",
"# 把 view 卸載\n",
"key_list = list(extno.keys())"
]
},
{
"cell_type": "code",
"execution_count": 10,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"dict_values([2567, 1234, 3080])\n"
]
}
],
"source": [
"# values() 的方法回傳一個 dict_values 的 view 物件，包含所有成員的 value\n",
"print(extno.values())\n",
"# 把 view 卸載\n",
"value_list = list(extno.values())"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 多種生成新的 `dict` 物件的方法\n",
"- `dict()`\n",
"- `dict.fromkeys()`\n",
"- `dict(zip())`\n",
"\n",
"Python 的內建函式 `zip()` 可以用來將多組序列物件裡的成員，按照對應順序分拆打包在一序列的 tuple 裡。`dict()` 會將每個 tuple 的第一個元素當成 key。"
]
},
{
"cell_type": "code",
"execution_count": 11,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"dict from key-value sequence = {'Brown': 2567, 'Cathy': 1234, 'Adam': 3080}\n"
]
}
],
"source": [
"# 可以從原本就是 key-value pair 的序列終生成\n",
"dict_from_view = dict(item_list)\n",
"print('dict from key-value sequence = {}'.format(dict_from_view))"
]
},
{
"cell_type": "code",
"execution_count": 12,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"dict from key list = {'Brown': 10000, 'Cathy': 10000, 'Adam': 10000}\n"
]
}
],
"source": [
"# fromkeys() 可以從 list 中生成新的字典容器，value 都用預設值\n",
"dict_from_keys = dict.fromkeys(key_list, 10000)\n",
"print('dict from key list = {}'.format(dict_from_keys))"
]
},
{
"cell_type": "code",
"execution_count": 13,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"\n",
"two lists after zipped: [(2567, 'Brown'), (1234, 'Cathy'), (3080, 'Adam')]\n"
]
}
],
"source": [
"# zip 把兩個 list 裡的成員分拆打包成 tuple 序列\n",
"print('\\ntwo lists after zipped: {}'.format(list(zip(value_list, key_list))))"
]
},
{
"cell_type": "code",
"execution_count": 14,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"dict from zipping 2 lists = {2567: 'Brown', 1234: 'Cathy', 3080: 'Adam'}\n"
]
}
],
"source": [
"# 新的 dict 用原本的 value 來當 key\n",
"dict_from_zip = dict(zip(value_list, key_list))\n",
"print('dict from zipping 2 lists = {}'.format(dict_from_zip))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 常用的 `dict` 物件方法"
]
},
{
"cell_type": "code",
"execution_count": 15,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"dict_from_view 有 3 個成員\n"
]
}
],
"source": [
"# 成員個數\n",
"print('dict_from_view 有 {} 個成員'.format(len(dict_from_view)))"
]
},
{
"cell_type": "code",
"execution_count": 16,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"\"Operator\" 不是 dict_from_view 的成員? (True)\n",
"dict_from_view[\"Operator\"] = 9999\n"
]
}
],
"source": [
"# get() 的方法常見用於讀取設定檔，沒有設定的參數就回傳預設值，不會沒有這個 key 就發生錯誤\n",
"print('\"Operator\" 不是 dict_from_view 的成員? ({})'.format('Operator' not in dict_from_view))\n",
"print('dict_from_view[\"Operator\"] = {}'.format(dict_from_view.get('Operator', 9999)))"
]
},
{
"cell_type": "code",
"execution_count": 17,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"\n",
"dict_from_view 的成員和 extno 都一樣嗎？ (True),\n",
"dict_from_view 是不是跟 extno 參考同一個物件？ (False)\n"
]
}
],
"source": [
"# 檢查從 view 裡產生的物件\n",
"print('\\ndict_from_view 的成員和 extno 都一樣嗎？ ({}),\\ndict_from_view 是不是跟 extno 參考同一個物件？ ({})'\n",
" .format(extno == dict_from_view, extno is dict_from_view))"
]
},
{
"cell_type": "code",
"execution_count": 18,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"\n",
"dict_from_copy 的成員和 extno 都一樣嗎？ (True),\n",
"dict_from_copy 是不是跟 extno 參考同一個物件？ (False)\n"
]
}
],
"source": [
"# 也可以用 copy() 複製一份新的 dict 物件\n",
"dict_from_copy = extno.copy()\n",
"print('\\ndict_from_copy 的成員和 extno 都一樣嗎？ ({}),\\ndict_from_copy 是不是跟 extno 參考同一個物件？ ({})'\n",
" .format(extno == dict_from_copy, extno is dict_from_copy))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## 7.1 Dict Comprehension\n",
"\n",
"對於可拆解出成對的 (key, value) 的序列容器或可迭代物件 S 進行操作，並生成一個新的 `dict` 物件。\n",
"\n",
"| 成員的操作 | 說明 |\n",
"|--------------------------------------------|---------------------------------------------------------------|\n",
"| `{key:value for (key,value) in S}` | 針對每個 S 的成員 x 做運算，運算結果生成新的 dict 物件 |\n",
"| `{key:value for (key,value) in S if 條件}` | 針對每個***符合條件***的成員 x 做運算，運算結果生成新的 dict 物件 |\n",
"\n",
"Dict comprehension 語法結構也可組成相當豐富的條件式迭代運算，但需注意`dict`容器的 *key* 不能重複，若重複指定不同 value 給同一個 key，結果對應的 value 會是最後指定的值。\n",
"```\n",
"{key:value運算表示句 for x1 in S1 if 條件1\n",
" for x2 in S2 if 條件2 ...\n",
" for xN in SN if 條件N}\n",
"```"
]
},
{
"cell_type": "code",
"execution_count": 19,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"{0: '0', 1: '1', 2: '2', 3: '3', 4: '4'}\n",
"{'a': 97, 'b': 98, 'c': 99}\n"
]
}
],
"source": [
"# 可迭代物件生成 dict 物件\n",
"print({x: str(x) for x in range(5)})\n",
"print({x: ord(x) for x in ['a', 'b', 'c']})"
]
},
{
"cell_type": "code",
"execution_count": 20,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"{0: 0, 2: 4, 4: 16, 6: 36, 8: 64}\n"
]
}
],
"source": [
"# 條件式挑選部份成員作處理\n",
"print({x: x ** 2 for x in range(10) if x % 2 == 0})"
]
},
{
"cell_type": "code",
"execution_count": 21,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"{1: 6, 2: 6, 3: 6}\n"
]
}
],
"source": [
"# 在 dict comprehension 使用巢狀迴圈，注意結果可能不如原先預期\n",
"print({k: v for k in range(1, 4) for v in range(4, 7)})"
]
},
{
"cell_type": "code",
"execution_count": 22,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"{0: 'd', 1: 'i', 2: 'c', 3: 't', 4: ' ', 5: 'c', 6: 'o', 7: 'm', 8: 'p', 9: 'r', 10: 'e', 11: 'h', 12: 'e', 13: 'n', 14: 's', 15: 'i', 16: 'o', 17: 'n'}\n"
]
}
],
"source": [
"# 使用 enumerate 把迭代次序當成 key\n",
"print({k: v for (k, v) in enumerate('dict comprehension')})"
]
},
{
"cell_type": "code",
"execution_count": 23,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"{'a': 1, 'b': 2, 'c': 3}\n"
]
}
],
"source": [
"# 可以使用 zip 兩兩配對\n",
"print({k: v for (k, v) in zip(['a', 'b', 'c'], [1, 2, 3])})"
]
}
],
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"file_extension": ".py",
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