python基礎資料型別 (Elementary Data Type)——str

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一、字串的建立

test = str() / ""test = str("licheng") / "licheng"

• 無參數，建立Null 字元串
• 一個參數，建立一般字元串
• 兩個參數，int（位元組，編碼）

二、字串的常用方法

#capitalize()：字串首字元大寫string = ‘this is a string.‘new_str = string.capitalize()print(new_str)#輸出：This is a string. #center(width, fillchar=None)：將字串放在中間，在指定長度下，首尾以指定輸入鍵台string = ‘this is a string.‘new_str = string.center(30,‘*‘)print(new_str)#輸出：******this is a string.******* #count(sub, start=None, end=None)：計算字串中某字元的數量string = ‘this is a string.‘new_str = string.count(‘i‘)print(new_str)#輸出：3 #decode/encode(encoding=None, errors=None)：解碼/解碼string = ‘this is a string.‘new_str = string.decode()new_str = string.encode()print(new_str) #endswith(self, suffix, start=None, end=None)：判斷是否以某字元結尾string = ‘this is a string.‘new_str = string.endswith(‘ing.‘)print(new_str)#輸出：True #find(self, sub, start=None, end=None)：在字串中尋找指定字元的位置string = ‘this is a string.‘new_str = string.find(‘a‘) #找的到的情況print(new_str)#輸出：8new_str = string.find(‘xx‘) #找不到的情況返回-1print(new_str)#輸出：-1 #index(self, sub, start=None, end=None)：；類似findstring = ‘this is a string.‘new_str = string.index(‘a‘) #找的到的情況print(new_str)#輸出：8new_str = string.index(‘xx‘) #找不到的情況，程式報錯print(new_str)#輸出：程式運行報錯，ValueError: substring not found #isalnum(self)：判斷字串中是否都是數字和字母，如果是則返回True，否則返回Falsestring = ‘My name is yue,my age is 18.‘new_str = string.isalnum()print(new_str)#輸出：Falsestring = ‘haha18121314lala‘new_str = string.isalnum()print(new_str)#輸出：True #isalpha(self)：判斷字串中是否都是字母，如果是則返回True，否則返回Falsestring = ‘abcdefg‘new_str = string.isalpha()print(new_str)#輸出：Truestring = ‘my name is yue‘new_str = string.isalpha() #字母中間帶空格、特殊字元都不行print(new_str)#輸出：False # isdigit(self)：判斷字串中是否都是數字，如果是則返回True，否則返回Falsestring = ‘1234567890‘new_str = string.isdigit()print(new_str)#輸出：Truestring = ‘haha123lala‘new_str = string.isdigit() #中間帶空格、特殊字元都不行print(new_str)#輸出：False # islower(self)：判斷字串中的字母是否都是小寫，如果是則返回True，否則返回Falsestring = ‘my name is yue,my age is 18.‘new_str = string.islower()print(new_str)#輸出：Truestring = ‘My name is Yue,my age is 18.‘new_str = string.islower()print(new_str)#輸出：False # isupper(self)：檢測字串中所有的字母是否都為大寫。string = ‘MY NAME IS YUE.‘new_str = string.isupper()print(new_str)#輸出：Truestring = ‘My name is Yue.‘new_str = string.isupper()print(new_str)#輸出：False # join(self, iterable)：將序列中的元素以指定的字元串連產生一個新的字串。string = ("haha","lala","ohoh")str = "-"print(str.join(string))#輸出：haha-lala-ohoh # lower(self)：轉換字串中所有大寫字元為小寫。string = "My Name is YUE."print(string.lower())# 輸出：my name is yue. # lstrip(self, chars=None)：截掉字串左邊的空格或指定字元。string = " My Name is YUE."print(string.lstrip())#輸出：My Name is YUE.string = "My Name is YUE."print(string.lstrip(‘My‘))#輸出： Name is YUE. #replace(self, old, new, count=None)：把字串中的 old（舊字串） 替換成 new(新字串)，如果指定第三個參數max，則替換不超過 max 次。string = "My name is yue."print(string.replace("yue","ying"))#輸出：My name is ying. # rfind(self, sub, start=None, end=None)：返回字串最後一次出現的位置，如果沒有匹配項則返回-1。string = "My name is yue."print(string.rfind(‘is‘))#輸出：8string = "My name is yue."print(string.rfind(‘XXX‘))#輸出：-1 # split(self, sep=None, maxsplit=None)：通過指定分隔字元對字串進行切片。string = "haha lala gege"print(string.split(‘ ‘))#輸出：[‘haha‘, ‘lala‘, ‘gege‘]print(string.split(‘ ‘, 1 ))#輸出： [‘haha‘, ‘lala gege‘] # rsplit(self, sep=None, maxsplit=None)：通過指定分隔字元對字串從右進行切片。string = "haha lala gege"print(string.rsplit(‘ ‘))#輸出：[‘haha‘, ‘lala‘, ‘gege‘]print(string.rsplit(‘ ‘, 1 ))#輸出： [‘haha lala‘, ‘gege‘] # rstrip(self, chars=None)：刪除 string 字串末尾的指定字元（預設為空白格）.string = " My name is yue. "print(string.rstrip())#輸出： My name is yue. # strip(self, chars=None)：移除字串頭尾指定的字元（預設為空白格）。string = " My name is yue. "print(string.strip())#輸出：My name is yue. # upper(self)：將字串中的小寫字母轉為大寫字母。string = "my name is yue,my age is 18."print(string.upper())#輸出：MY NAME IS YUE,MY AGE IS 18.

 str源碼三、字串的公用功能

• 索引（只能取一個元素）
• 切片（取多個元素）
• 長度（len）
  • python2：按位元組算長度
  • python3：按字元算長度
• for迴圈（同長度的版本迴圈單位）

四、字元與位元組的轉換

# 將gbk編碼的字元轉化為位元組s = "李程"b = bytes(s, encoding="gbk")type(b)  輸出為位元組類型# 將位元組轉化為字元c = str(b, encoding="gbk")

五、字串格式化

Python的字串格式化有兩種方式: 百分比符號方式、format方式

百分比符號的方式相對來說比較老，而format方式則是比較先進的方式，企圖替換古老的方式，目前兩者並存。

1、百分比符號方式

%[(name)][flags][width].[precision]typecode

 參數詳解

常用格式化：

tpl = "i am %s" % "spark" tpl = "i am %s age %d" % ("spark", 18) tpl = "i am %(name)s age %(age)d" % {"name": "spark", "age": 18} tpl = "percent %.2f" % 99.97623 tpl = "i am %(pp).2f" % {"pp": 123.425556, } tpl = "i am %.2f %%" % {"pp": 123.425556, }

2、Format方式

[[fill]align][sign][#][0][width][,][.precision][type]

 參數詳解

 常用格式化：

 1 tpl = "i am {}, age {}, {}".format("seven", 18, ‘alex‘) 2    3 tpl = "i am {}, age {}, {}".format(*["seven", 18, ‘alex‘]) 4    5 tpl = "i am {0}, age {1}, really {0}".format("seven", 18) 6    7 tpl = "i am {0}, age {1}, really {0}".format(*["seven", 18]) 8    9 tpl = "i am {name}, age {age}, really {name}".format(name="seven", age=18)10   11 tpl = "i am {name}, age {age}, really {name}".format(**{"name": "seven", "age": 18})12   13 tpl = "i am {0[0]}, age {0[1]}, really {0[2]}".format([1, 2, 3], [11, 22, 33])14   15 tpl = "i am {:s}, age {:d}, money {:f}".format("seven", 18, 88888.1)16   17 tpl = "i am {:s}, age {:d}".format(*["seven", 18])18   19 tpl = "i am {name:s}, age {age:d}".format(name="seven", age=18)20   21 tpl = "i am {name:s}, age {age:d}".format(**{"name": "seven", "age": 18})22  23 tpl = "numbers: {:b},{:o},{:d},{:x},{:X}, {:%}".format(15, 15, 15, 15, 15, 15.87623, 2)24  25 tpl = "numbers: {:b},{:o},{:d},{:x},{:X}, {:%}".format(15, 15, 15, 15, 15, 15.87623, 2)26  27 tpl = "numbers: {0:b},{0:o},{0:d},{0:x},{0:X}, {0:%}".format(15)28  29 tpl = "numbers: {num:b},{num:o},{num:d},{num:x},{num:X}, {num:%}".format(num=15)

更多格式化操作：https://docs.python.org/3/library/string.html

python基礎資料型別 (Elementary Data Type)——str