e.Python - 字串(String)

# e.Python - 字串(String) ###### tags: `Python` ## 1.字串(String) * **字串為字元序列** ```python=+ x = "Hello" print(x[0]) print(x[-1]) print(x[1:]) print(len(x)) ``` > ```H``` > ```o``` > ```ello``` > ```5``` ## * **字串物件修改** ```python=+ x = "GoodBye~" print(x,id(x)) x = x[:-1] #字串不能修改，會直接成為新物件 print(x,id(x)) ``` > ```GoodBye~ 1928774669296``` > ```GoodBye 1928774658672``` ## 2.基本的字串操作(String) * **連接多個字串** ```python=+ x = "Hello " + "World" print(x) x = "Hello " "World" #自動將多個空白相隔的字串連接在一起 print(x) ``` > ```Hello World``` > ```Hello World``` ## 3.特殊字元和轉義字元 * **基本轉義字元** | 類別 | 說明 | | :------: | :-----------: | | \\' | 單引號(')| | \\" | 雙引號(") | | \\\\ | 反斜線(\\) | | \\a | 發出嗶聲(Bell) | | \\b | 倒退鍵(Backspace) | | \\f | 換頁 | | \\n | 換行 | | \\r | 歸位符號(Carriage Return) | | \\t | 定位符號(Tab) | | \\v | 垂直定位符號(Vertical Tab) | ## * **數值(八進位和十六進位)表示** ```python=+ 'm' '\155' #八進位轉義字元 '\x6D' #十六進位轉義字元(大小寫皆可) ``` > ```'m'``` > ```'m'``` > ```'m'``` ## * **轉義字元表示** ```python=+ '\n' #換行符號 '\012' #八進位轉義字元 '\x0A' #十六進位轉義字元(大小寫皆可) ``` > ```'\n'``` > ```'\n'``` > ```'\n'``` ## * **Unicode字串表示** > **Python 3中所有的字串都是Unicode字串** ```python=+ #透過Unicode名稱，表示Unicode字元 unicode_a = '\N{LATIN SMALL LETTER A}' unicode_a unicode_a_with_acute = '\N{LATIN SMALL LETTER A WITH ACUTE}' unicode_a_with_acute "\u00E1" #透過\u後面跟著4碼16進位數字表示Unicode字元 ``` > ```'a'``` > ```'á'``` > ```'á'``` ## 4.字串常用的 Method 與函式 * **join()** ```python=+ x = " ".join(['HI,','my','name','is','ZEOxO','!!']) print(x) ``` > ```HI, my name is ZEOxO !!``` ## * **split()** ```python=+ x = 'HI, \t\tmy \nname \tis \n\rZEOxO !!' print(x.split()) #預設為切割空白字元(空格、換行、定位等) x = 'Mississippi' print(x.split('ss')) x = 'a b c d' print(x.split(' ',2)) print(x.split(' ',9)) x = 'a\nb c d' print(x.split(' ',2)) #指定只切「空白」字元(不會切轉義字元) print(x.split(None,2)) #不指定，則會切轉義字元 ``` > ```['HI,', 'my', 'name', 'is', 'ZEOxO', '!!']``` > ```['Mi', 'i', 'ippi']``` > ```['a', 'b','c d']``` > ```['a', 'b', 'c', 'd']``` > ```['a\nb', 'c', 'd']``` > ```['a', 'b', 'c d']``` ## * **float() 將字串轉為浮點數** ```python=+ float('123.456') float('123') float('xxyy') ``` > ```123.456``` > ```123.0``` > ```ValueError: could not convert string to float: 'xxyy'``` ## * **int() 將字串轉為數字** ```python=+ int('3333') int('123.456') #不可有小數點 int('10000',8) #用8進位的基底來解釋10進位整數(10000) int('101',2) #用2進位的基底來解釋10進位整數(101) int('ff',16) #用16進位的基底來解釋10進位整數(ff) int('123456',6) #6進位為「0~5」，不應包含「6」 ``` > ```3333``` > ```ValueError: invalid literal for int() with base 10: '123.456'``` > ```4096``` > ```5``` > ```255``` > ```ValueError: invalid literal for int() with base 6: '123456'``` ## * **strip()、lstrip()、rstrip()** ```python=+ x = ' Hello World\t\t' x.strip() x.lstrip() x.rstrip() ``` > ```'Hello World'``` > ```'Hello World\t\t'``` > ```' Hello World'``` ## * **strip() 指定字元** ```python=+ x = 'www.python.org' x.strip('w') x.strip('.gorw') x.strip("go") x.strip("gr") ``` > ```.python.org``` > ```python``` > ```www.python.or``` > ```www.python.o``` ## * **isdigit()、isalpha()、islower()、isupper()** ```python=+ x = '123' x.isdigit() x.isalpha() x = 'MM' x.islower() x.isupper() ``` > ```True``` > ```False``` > ```False``` > ```True``` ## 5.字串的搜尋 * **in 算符** ```python=+ x = 'The string' print('str' in x) print('sTr' in x) print('e s' in x) ``` > ```True``` > ```False``` > ```True``` ## * **find()、rfind()、index()、rindex()** ```python=+ x = 'Mississippi' print(x.find('is')) print(x.find('zz')) #不存在傳回-1 print(x.find('s',2)) #從指定索引值開始搜尋 print(x.find('s',4,5)) #到指定索引值之前停止搜尋 print(x.find('ss',3)) print(x.find('ss',0,3)) print(x.rfind('ss')) #index和rindex與find、rfind相同，但找不到文字時會引發例外錯誤 ``` > ```1``` > ```-1``` > ```2``` > ```-1``` > ```5``` > ```-1``` > ```5``` ## * **count()** ```python=+ x = "Mississippi" x.count('ss') ``` > ```2``` ## * **startswith()、endswith()** ```python=+ x = "Mississippi" print(x.startswith('Miss')) print(x.endswith('pp')) print(x.endswith(('i','u'))) #可以tuple形式傳入多筆搜尋文字 ``` > ```True``` > ```False``` > ```True``` ## 6.字串的修改 * **replace()** ```python=+ x = "Mississippi" x.replace('ss','zzz') ``` > ```'Mizzzizzzippi'``` ## * **maketrans()、translate()** ```python=+ x = '~x ^ (y % z)' table = x.maketrans('~^()','!&[]') print(table) x.translate(table) ``` > ```{126: 33, 94: 38, 40: 91, 41: 93}``` > ```'!x & [y % z]'``` ## * **capitalize()、title()** ```python=+ x = 'hi, my name is ZEOxO !!' print(x.capitalize()) #將字串的第一個字元為大寫、其餘小寫 print(x.title()) #將所有單字的第一個字元為大寫、其餘小寫 ``` > ```Hi, my name is zeoxo !!``` > ```Hi, My Name Is Zeoxo !!``` ## * **<!>swapcase()、expandtabs()** ```python=+ x = 'hi,\tmy\tname\tis\tZEOxO !!' print(x.swapcase()) #將字串內所有字母大寫轉小寫、小寫轉大寫 print(x.expandtabs(1)) #將字串內定位符號轉為指定數目的空格(如1個空格) ``` > ```HI, 　MY 　NAME 　is 　zeoXo !!``` > ```hi, my name is ZEOxO !!``` ## * **ljust()、rjust()** ```python=+ x = 'Hello World' print(x.ljust(20,'!')) print(x.rjust(20,'!')) print(x.center(20,'!')) ``` > ```Hello World!!!!!!!!!``` > ```!!!!!!!!!Hello World``` > ```!!!!Hello World!!!!!``` ## 7.字串的格式化輸出 * **指名參數格式化輸出(format)** ```python=+ st = '{0:10} are often called the "king of the beasts".'.format("Lion") st = '{0:>10} are often called the "king of the beasts".'.format("Lion") st = '{0:#>10} are often called the "king of the beasts".'.format("Lion") ``` > ```Lion are often called the "king of the beasts".``` > ```　　　 Lion are often called the "king of the beasts".``` > ```######Lion are often called the "king of the beasts".``` ## * **指名參數格式化輸出(字典)** ```python=+ "NO.{rank} is {name}!!".format(name = 'ZEOxO',rank = '1') ``` > ```'NO.1 is ZEOxO!!'``` ## * **<!>指名參數格式化輸出(陣列)** ```python=+ "User name:{info[0]} ID:{info[1]} addr:{info[2]}".format(info = ['ZEOxO','123456','Taipei']) ``` > ```'User name:ZEOxO ID:123456 addr:Taipei'``` ## 8.其他常用及特殊的 String 操作 * **repr()、str()將物件轉換成字串表示** ```python=+ repr([1,2,3]) x = [1] x.append(2) x.append([3,4]) 'the list x is ' + repr(x) ``` > ```'[1, 2, 3]'``` > ```'the list x is [1, 2, [3, 4]]'``` ## * **repr() 傳入物件參數** > **<!>repr非常適合用來程式除錯** ```python=+ repr(print)#將系統內建方法、物件作為參數傳入 repr(str.upper) ``` > ```'<built-in function print>'``` > ```'<method 'upper' of 'str' objects>'``` ## * **(續)repr() 傳入物件參數** ```python=+ from datetime import datetime now = datatime.now() now str(now) repr(now) ``` > ```'2020-08-26 15:18:40.695042'``` > ```'2020-08-26 15:18:40.695042'``` > ```'datetime.datetime(2020, 8, 26, 15, 18, 40, 695042)'``` ## * **repr() 的文字範例** ```python=+ tb="物品\t數量\t售價\n蘋果\t1\t25" print(tb) print('\n') print(repr(tb)) #可以看到格式字符 ``` > ```物品數量售價``` >```蘋果 1 25``` > ```'物品\t數量\t售價\n蘋果\t1\t25'``` ## 9.Python 字串模組 * **<!>被 Python 定義的空白字元** ```python=+ import string string.whitespace #可透過存取「string.whitespace」常數找到 ' \t\n\r\v\f' #指的就是這些字元符號 ``` > ```' \t\n\r\x0b\x0c'``` > ```' \t\n\r\x0b\x0c'``` ## * **(!)其他被 Python 定義的字元** ```python=+ import string string.digits string.hexdigits string.octdigits string.ascii_lowercase string.ascii_uppercase string.ascii_letters #包含lowercase和uppercase所有字元 ``` > ```'0123456789'``` > ```'0123456789abcdefABCDEF'``` > ```'01234567'``` > ```'abcdefghijklmnopqrstuvwxyz'``` > ```'ABCDEFGHIJKLMNOPQRSTUVWXYZ'``` > ```'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'``` ## 時間戳記 > [name=ZEOxO][time=Wed, Aug 26, 2020 16:00 PM][color=#907bf7]