{
"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/04-String_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/04-String_Operations.ipynb)\n",
"\n",
"\n",
"# 4. `str` 字串操作\n",
"\n",
"`str` 字串是以字元為元素的序列資料結構，字串的語法使用單引號或雙引號包起來，一樣的引號要成對使用。\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",
"| 字串範例 | 說明 |\n",
"|------------------------------|-----------------------------------------------|\n",
"| `''` | 空字串 |\n",
"| `\"Python's\"`, `'Python\"s'` | 字串用單引號或雙引號包起來 |\n",
"| `'Python\\'s\\n'` | 特殊字元前面要加反斜線 `\\` |\n",
"| `r'c:\\Users\\name'` | 引號前置碼`r`保留字串呈現的原貌（raw string） |\n",
"| `\"This\" \"is\" \"concatenated\"` | 相鄰的字串會自動被串接起來 |\n",
"\n",
"- 內建函式 `str()` 用來建構新字串，或將物件轉成字串。\n",
"- 內建函式 `hex()`、`bin()` 分別可以用來將數值轉換成十六進位及二進位的數字字串。\n",
"- 內建函式 `chr()` 可以用來將字碼轉換成對應的字元，是 `ord()` 的逆向操作。\n",
"- 內建函式 `len()` 可以用來回傳字串的長度。\n",
"- 內建函式 `print()` 可以用來將字串內容輸出至畫面。\n",
"\n",
"字串類別本身有很多專屬的方法，請參閱官方文件 [Text Sequence Type — str](https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str)。以下僅列出常用的幾個：\n",
"- `format()` 用來格式化字串。\n",
"- `count()` 計算某個子字串出現幾次。\n",
"- `find()` 找出子字串出現的位置。\n",
"- `lower()` 返回全部是小寫的複本。\n",
"- `upper()` 返回全部是大寫的複本。\n",
"- `replace()` 將子字串全部替換成指定的字串。\n",
"- `split()` 將字串按照指定的分隔符號切割。\n",
"- `strip()` 移除字串前後的空白字元。\n",
"\n",
"字串也是序列容器，所以一般 immutable 序列容器的共同方法也都可以用，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": [
"### § 字串是不能就地變更的序列容器。\n",
"\n",
"字串在建立後，元素內容**不可以**就地變更（immutable）。"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [
{
"ename": "TypeError",
"evalue": "'str' 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-1-18ce7d0609eb>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m 1\u001b[0m \u001b[1;31m# 對字串元素指定新值會造成錯誤\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m 2\u001b[0m \u001b[0ms\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'Pithon'\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[0ms\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m]\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'y'\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[1;31mTypeError\u001b[0m: 'str' object does not support item assignment"
]
}
],
"source": [
"# 對字串元素指定新值會造成錯誤\n",
"s = 'Pithon'\n",
"s[1] = 'y'"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 透過切割、重複複製、及串接的操作可以產生新字串。"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Python\n"
]
}
],
"source": [
"# 使用 [from:to:interval] 的語法切割片段範圍\n",
"# 使用加號 '+' 串接字串\n",
"s = s[0] + 'y' + s[2:]\n",
"print(s)"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Python Python Python rocks!\n"
]
}
],
"source": [
"# 使用乘號 '*' 重複複製序列元素\n",
"s = 3 * (s + ' ') + 'rocks!'\n",
"print(s)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 讀取某位置的索引值不能超過範圍，但片段的指定可以容許超過範圍。"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"length of string is 27\n"
]
},
{
"ename": "IndexError",
"evalue": "string index out of range",
"output_type": "error",
"traceback": [
"\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[1;31mIndexError\u001b[0m Traceback (most recent call last)",
"\u001b[1;32m<ipython-input-4-b72f16fd5655>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m 1\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m'length of string is '\u001b[0m \u001b[1;33m+\u001b[0m \u001b[0mstr\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mlen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0ms\u001b[0m\u001b[1;33m)\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[0;32m 2\u001b[0m \u001b[1;31m# 超出索引值範圍會造成錯誤\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[0ms\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m60\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[1;31mIndexError\u001b[0m: string index out of range"
]
}
],
"source": [
"print('length of string is ' + str(len(s)))\n",
"# 超出索引值範圍會造成錯誤\n",
"s[60]"
]
},
{
"cell_type": "code",
"execution_count": 5,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"'rocks!'"
]
},
"execution_count": 5,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"# 指定的片段不存在返回空字串\n",
"s[21:60]"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § 字串類別本身有許多好用的方法，可以用來操作子字串"
]
},
{
"cell_type": "code",
"execution_count": 6,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"There are 3 spaces\n"
]
}
],
"source": [
"# 數一數字串裡有幾個空格字元\n",
"print('There are ' + str(s.count(' ')) + ' spaces')"
]
},
{
"cell_type": "code",
"execution_count": 7,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"New comma separated string is: Python,Python,Python,rocks!\n"
]
}
],
"source": [
"# 將空格字元用逗號取代\n",
"s = s.replace(' ', ',')\n",
"print('New comma separated string is: ' + s)"
]
},
{
"cell_type": "code",
"execution_count": 8,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"['Python', 'Python', 'Python', 'rocks!']\n"
]
}
],
"source": [
"# 將逗號分隔的片段切割成子串\n",
"print(s.split(sep = ','))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## 4.1 用 `format()` 格式化字串\n",
"使用大括號 `{` `}` 保留需要格式化字串的位置，裡面可以指定欄位名稱及格式規則。（註: 以下格式是簡化過的版本，完整的定義請參閱官方文件 [6.1.3. Format String Syntax](https://docs.python.org/3/library/string.html#format-string-syntax)）\n",
"<p>\n",
" <center>格式化語法： <b>`{` `欄位名稱` `:格式規則` `}`</b></center>\n",
"</p>\n",
"\n",
"- `欄位名稱`：可以用數字或文字命名。欄位名字所在的位置，會被指定用某個格式化後的文字取代。\n",
"- `格式規則`：指定用來從原物件資料轉成字串的規則，如欄位寬、小數點位數、左右對齊等。格式的規則按照以下語法順序指定，中括號不是語法的一部份，只是用來區隔每一種可有可無的格式選項：\n",
"\n",
"<p>\n",
" <center>格式規則順序： [[`空白填補字元`]`對齊`] [`#`] [`0`] [`寬度`] [`.小數點精度`] [`格式類型`]</center>\n",
"</p>\n",
"\n",
"- `對齊`\n",
"\n",
"| 對齊選項 | 說明 |\n",
"|-----------|-----------|\n",
"| **`<`** | 靠左對齊 |\n",
"| **`>`** | 靠右對齊 |\n",
"| **`^`** | 置中 |\n",
"\n",
"- `#`：指定顯示數值進制的前綴符號。\n",
"- `0`：針對數值格式，指定在空白處補 `'0'`。\n",
"- `寬度`：指定欄位寬。\n",
"- `.小數點精度`：指定小數點後面幾位數\n",
"- `格式類型`\n",
"\n",
"| 格式類型 | 說明 |\n",
"|-----------|-----------|\n",
"| **`s`** | 字串 |\n",
"| **`c`** | 字元 |\n",
"| **`b`** | 二進位 |\n",
"| **`d`** | 十進制整數 |\n",
"| **`x`** | 小寫字母十六進制整數 |\n",
"| **`X`** | 大寫字母十六進制整數 |\n",
"| **`f`** | 浮點數，預設小數點以下6位 |\n",
"| **`e`** | 小寫字母科學記號 |\n",
"| **`E`** | 大寫字母科學記號 |\n",
"| **`%`** | 將浮點數轉換為百分比 |"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § `format` 指定欄位名稱"
]
},
{
"cell_type": "code",
"execution_count": 9,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Math constants: π = 3.141592653589793, e = 2.718281828459045, τ = 6.283185307179586\n"
]
}
],
"source": [
"import math\n",
"# 用數字指定欄位名字，數字對應的是format()裡的參數順序\n",
"print('Math constants: π = {0}, e = {1}, τ = {2}'.format(math.pi, math.e, math.tau))"
]
},
{
"cell_type": "code",
"execution_count": 10,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Math constants: π = 3.141592653589793,\n",
" τ = 6.283185307179586, \tτ 其實就是 2π = 2 * 3.141592653589793\n"
]
}
],
"source": [
"# 欄位可以重複指定使用\n",
"print('Math constants: π = {0},\\n τ = {1}, \\tτ 其實就是 2π = 2 * {0}'.format(math.pi, math.tau))"
]
},
{
"cell_type": "code",
"execution_count": 11,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Math constants: π = 3.141592653589793, e = 2.718281828459045, τ = 6.283185307179586\n"
]
}
],
"source": [
"# 數字欄位的名字可以不用照順序\n",
"print('Math constants: π = {2}, e = {0}, τ = {1}'.format(math.e, math.tau, math.pi))"
]
},
{
"cell_type": "code",
"execution_count": 12,
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"'Math constants: π = 3.141592653589793, e = 2.718281828459045, τ = 6.283185307179586'"
]
},
"execution_count": 12,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"# 如果全部欄位都按照順序，一個蘿蔔一個坑，那欄位裡的數字可以省略\n",
"'Math constants: π = {}, e = {}, τ = {}'.format(math.pi, math.e, math.tau)"
]
},
{
"cell_type": "code",
"execution_count": 13,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Math constants: π = 3.141592653589793, e = 2.718281828459045, τ = 6.283185307179586\n"
]
}
],
"source": [
"# 用文字指定欄位名字，而因為format()裡也明確指定參數的名字，所以參數列出來的順序就不重要了\n",
"print('Math constants: π = {Pi}, e = {e}, τ = {Tau}'.format(e=math.e, Pi=math.pi, Tau=math.tau))"
]
},
{
"cell_type": "code",
"execution_count": 14,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Math constants: π = 3.141592653589793, τ = 6.283185307179586, τ 其實就是 2π = 2 * 3.141592653589793\n"
]
}
],
"source": [
"# 欄位可以重複指定使用\n",
"print('Math constants: π = {Pi}, τ = {Tau}, τ 其實就是 2π = 2 * {Pi}'.format(Pi=math.pi, Tau=math.tau))"
]
},
{
"cell_type": "code",
"execution_count": 15,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Math constants: 3.141592653589793, 2.718281828459045, 6.283185307179586\n"
]
}
],
"source": [
"m = [math.pi, math.e, math.tau]\n",
"# list 卸載會塞到對應順序的欄位\n",
"print('Math constants: {}, {}, {}'.format(*m))"
]
},
{
"cell_type": "code",
"execution_count": 16,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Math constants: π = 3.141592653589793, τ = 6.283185307179586, e = 2.718281828459045\n",
"Math constants: pi, e, tau\n"
]
}
],
"source": [
"n = {'pi': math.pi, 'e': math.e, 'tau': math.tau}\n",
"# dict 卸載會塞value到對應key的欄位\n",
"print('Math constants: π = {pi}, τ = {tau}, e = {e}'.format(**n))\n",
"# 或是只卸載 key\n",
"print('Math constants: {}, {}, {}'.format(*n))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § `format` 指定寬度、對齊與空白填補"
]
},
{
"cell_type": "code",
"execution_count": 17,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"left aligned------------------\n"
]
}
],
"source": [
"# 靠左，空白處補 '-'\n",
"print('{:-<30}'.format('left aligned'))"
]
},
{
"cell_type": "code",
"execution_count": 18,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
" right aligned\n"
]
}
],
"source": [
"# 靠右\n",
"print('{:>30}'.format('right aligned'))"
]
},
{
"cell_type": "code",
"execution_count": 19,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"***********centered***********\n"
]
}
],
"source": [
"# 置中，空白處補 '*'\n",
"print('{:*^30}'.format('centered'))"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"### § `format` 指定數值格式與小數精度"
]
},
{
"cell_type": "code",
"execution_count": 20,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"int: 42; hex: 2a; oct: 52; bin: 101010\n"
]
}
],
"source": [
"# 沒有進制前綴符號\n",
"print('int: {0:d}; hex: {0:x}; oct: {0:o}; bin: {0:b}'.format(42))"
]
},
{
"cell_type": "code",
"execution_count": 21,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"int: 42; hex: 0x2a; oct: 0o52; bin: 0b101010\n"
]
}
],
"source": [
"# 加上進制前綴符號\n",
"print('int: {0:d}; hex: {0:#x}; oct: {0:#o}; bin: {0:#b}'.format(42))"
]
},
{
"cell_type": "code",
"execution_count": 22,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"constant π = 3.1400000000000000000000000000\n"
]
}
],
"source": [
"# 改變小數精度\n",
"print('constant π = {0:<030.2f}'.format(math.pi))"
]
},
{
"cell_type": "code",
"execution_count": 23,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"constant π = 00000000000000000000003.14e+00\n"
]
}
],
"source": [
"# 改變數值顯示格式\n",
"print('constant π = {0:>030.2e}'.format(math.pi))"
]
},
{
"cell_type": "code",
"execution_count": 24,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"π% = 314.159%\n"
]
}
],
"source": [
"# 用百分比顯示\n",
"print('π% = {:.3%}'.format(math.pi))"
]
}
],
"metadata": {
"kernelspec": {
"display_name": "Python 3",
"language": "python",
"name": "python3"
},
"language_info": {
"codemirror_mode": {
"name": "ipython",
"version": 3
},
"file_extension": ".py",
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