一、字符串
1、定义和初始化
In [4]: s = "hello python"
In [4]: s = "hello python"
In [5]: s
Out[5]: 'hello python'
In [6]: s = 'hello python'
In [7]: s
Out[7]: 'hello python'
In [8]: s = '''hello python'''
In [9]: s
Out[9]: 'hello python'
In [10]: s = """hello python"""
In [11]: s
Out[11]: 'hello python' python 中单双引号没有区别，只能定义单行字符串
三引号能定义多行字符串
单双三引号是有区别的 In [24]: s = 'hello python
File "<ipython-input-24-54fb5309d2d0>", line 1
s = 'hello python
^
SyntaxError: EOL while scanning string literal
In [25]: s = 'hello python \ # 续写上一行
...: i like python'
In [26]: s
Out[26]: 'hello python i like python'
In [22]: s = """hello python
...: i like python"""
In [23]: s
Out[23]: 'hello python\ni like python'工厂函数 str()：
In [12]: print(str.__doc__)
str(object='') -> str
str(bytes_or_buffer[, encoding[, errors]]) -> str
Create a new string object from the given object. If encoding or
errors is specified, then the object must expose a data buffer
that will be decoded using the given encoding and error handler.
Otherwise, returns the result of object.__str__() (if defined)
or repr(object).
encoding defaults to sys.getdefaultencoding().
errors defaults to 'strict'.
In [13]: s = str("abc")
In [14]: s
Out[14]: 'abc'
In [16]: s = str([1, 2])
In [17]: s
Out[17]: '[1, 2]'
In [18]: s = str(1)
In [19]: s
Out[19]: '1'2、字符串本义
In [32]: s = "i like \n python"
In [33]: s
Out[33]: 'i like \n python'
In [34]: s = "i like \npython"
In [35]: s
Out[35]: 'i like \npython'
In [36]: s = 'I'm xj'File"<ipython-input-36-0b8827686244>", line 1
s = 'I'm xj'
^
SyntaxError: invalid syntax
In [37]: s = 'I\'m xj'
In [38]: s
Out[38]: "I'm xj"In [50]: path ='c:\windows\nt\system32' # 这里的 \n 可能会被本义成换行符
In [51]: path
Out[51]: 'c:\\windows\nt\\system32'
In [52]: path = 'c:\\windows\\nt\\system32' # 个别须要这么写
In [53]: path
Out[53]: 'c:\\windows\\nt\\system32'
In [54]: path = r'c:\windows\nt\system32' # 加 r（raw）能示意此字符串是天然字符串，不会本义
In [55]: path
Out[55]: 'c:\\windows\\nt\\system32'二、字符串的操作
1、索引操作
In [59]: s = "I'm xjj"
In [60]: s[1]
Out[60]: "'"
In [61]: s[2]
Out[61]: 'm'
In [62]: s[3]
Out[62]: ' '2、str 的连贯和宰割
1）str 的连贯
str.join()
应用 str 将可迭代对象的 str 元素连接成 1 个 str
参数是元素都为 str 的可迭代对象，接收者是分隔符
In [71]: print(str.join.__doc__)
S.join(iterable) -> str
Return a string which is the concatenation of the strings in the
iterable. The separator between elements is S.
In [81]: lst = ["I", "am", "xxj"] # 可迭代对象的元素必须是 str
In [82]: ''.join(lst)
Out[82]: 'Iamxxj'
In [83]: ' '.join(lst)
Out[83]: 'I am xxj'
In [84]: ','.join(lst)
Out[84]: 'I,am,xxj'
In [85]: ',!'.join(lst)
Out[85]: 'I,!am,!xxj'
In [86]: ','.join(lst)
Out[86]: 'I , am , xxj'
In [87]: lst = [1, 2, 3]
In [88]: ','.join(lst)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-88-b4c772e35459> in <module>()
----> 1 ','.join(lst)
TypeError: sequence item 0: expected str instance, int found+
In [93]: "hello" + "python"
Out[93]: 'hellopython'
In [94]: str1 = "xxj"
In [95]: str1 + 1
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-95-2584ac008f78> in <module>()
----> 1 str1 + 1
TypeError: must be str, not int
In [96]: str1 + "hello"
Out[96]: 'xxjhello'
In [97]: str1 + "hello"
Out[97]: 'xxj hello'2）宰割
str.split()
不原地批改，返回应用分隔符分隔的列表
In [99]: print(s.split.__doc__)
S.split(sep=None, maxsplit=-1) -> list of strings
Return a list of the words in S, using sep as the
delimiter string. If maxsplit is given, at most maxsplit
splits are done. If sep is not specified or is None, any
whitespace string is a separator and empty strings are
removed from the result.
In [98]: s = "I love python"
In [100]: s.split("o") # 默认分隔所有
Out[100]: ['I l', 've pyth', 'n']
In [101]: s.split("o", 1) # 指定分隔一次
Out[101]: ['I l', 've python']
In [102]: s.split()
Out[102]: ['I', 'love', 'python']
In [102]: s.split() # 默认分隔符为 1 个或多个空格
Out[102]: ['I', 'love', 'python']
In [103]: s.split("ov") # 能够应用多个字符串当空格
Out[103]: ['I l', 'e python']
In [159]: s.split("A") # 不蕴含分隔符号时，不分隔原 str
Out[159]: ['I love python']
In [104]: s = "I love python"
In [105]: s.split()
Out[105]: ['I', 'love', 'python']
In [108]: s.split(" ") # 应用一个空格当做分隔符
Out[108]: ['I', 'love', '','', '','', '','python']
In [110]: s.split(maxsplit=1)
Out[110]: ['I', 'love python']
In [111]: s.split()
Out[111]: ['I', 'love', 'python']str.rsplit()：
从右往左开始分隔；
当不指定 maxsplit 参数时，str.rsplit() 和 str.split() 齐全一样，当 str.split() 效率更高
In [122]: s = "I love python"
In [123]: s.rsplit("o")
Out[123]: ['I l', 've pyth', 'n']
In [124]: s.rsplit("o", 1)
Out[124]: ['I love pyth', 'n']str.splitlines():
按行分隔，返回后果能够抉择带不带换行符；返回值是一个列表 In [136]: print(str.splitlines.__doc__)
S.splitlines([keepends]) -> list of strings
Return a list of the lines in S, breaking at line boundaries.
Line breaks are not included in the resulting list unless keepends
is given and true.
In [137]: s = """I am xxj
...: i love python"""
In [138]: s
Out[138]: 'I am xxj\ni love python'
In [139]: s.splitlines()
Out[139]: ['I am xxj', 'i love python']
In [140]: s.splitlines(true)
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-140-dfaf8d28775c> in <module>()
----> 1 s.splitlines(true)
NameError: name 'true' is not defined
In [141]: s.splitlines(True)
Out[141]: ['I am xxj\n', 'i love python']str.partition()：
总是返回一个三元组，它被传入的分隔符分隔 1 次，分隔成（head, sep,tail）
In [145]: print(str.partition.__doc__)
S.partition(sep) -> (head, sep, tail)
Search for the separator sep in S, and return the part before it,
the separator itself, and the part after it. If the separator is not
found, return S and two empty strings.
In [147]: s = "I love python"
In [148]: s.partition("o")
Out[148]: ('I l', 'o', 've python')str.rpartition() 是 str.partition() 从右往左的版本：
In [153]: s.rpartition("o")
Out[153]: ('I love pyth', 'o', 'n')
In [154]: s.rpartition("A")
Out[154]: ('','', 'I love python')
In [155]: "A".rpartition("A")
Out[155]: ('','A','')
In [156]: "".rpartition("A")
Out[156]: ('','', '')
In [157]: "".rpartition("A")
Out[157]: ('','', ' ')3、str 大小写转换与排版
In [2]: s = "I love python"
In [3]: s.upper()
Out[3]: 'I LOVE PYTHON'
In [5]: s.lower()
Out[5]: 'i love python'
In [6]: s.title() # 首字母全副大写
Out[6]: 'I Love Python'
In [8]: s.capitalize() # 把首字母大写
Out[8]: 'I love python'
In [10]: print(s.center.__doc__) # 在给定宽度下居中，能够应用单个字符填充
S.center(width[, fillchar]) -> str
Return S centered in a string of length width. Padding is
done using the specified fill character (default is a space)
In [11]: s.center(50)
Out[11]: 'I love python'
In [12]: s.center(50, "#")
Out[12]: '##################I love python###################'
In [13]: s.center(50, "#%")
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-13-4aa39ce1c3b3> in <module>()
----> 1 s.center(50, "#%")
TypeError: The fill character must be exactly one character long
In [19]: s
Out[19]: 'I love python'
In [20]: s.zfill(5)
Out[20]: 'I love python'
In [21]: s.zfill(50) # 用 0 填充
Out[21]: '0000000000000000000000000000000000000I love python'
In [23]: print(s.casefold.__doc__)
S.casefold() -> str
Return a version of S suitable for caseless comparisons.
In [25]: s
Out[25]: 'I love python'
In [26]: s.casefold() # 返回一个对立大小写的 str，在不同平台有不同的表现形式
Out[26]: 'i love python'
In [27]: s.swapcase() # 替换大小写
Out[27]: 'i LOVE PYTHON'
In [36]: "\t".expandtabs() # 默认将 \t 转换为 8 个空格
Out[36]: ' '
In [40]: "\t".expandtabs(8)
Out[40]: ' '
In [37]: "\t".expandtabs(3)
Out[37]: ' '4、批改
str.replace()
应用 new str 替换 old str，返回新的 str
In [44]: help(str.replace.__doc__)
No Python documentation found for 'S.replace(old, new[, count]) -> str\n\nReturn a copy of S with all occurrences of substring\nold replaced by new. If the optional argument count is\ngiven, only the first count occurrences are replaced.'.
Use help() to get the interactive help utility.
Use help(str) for help on the str class.
In [47]: s
Out[47]: 'I love python'
In [48]: s.replace("love", "give up")
Out[48]: 'I give up python'
In [49]: s.replace("o", 0)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-49-184707d40696> in <module>()
----> 1 s.replace("o", 0)
TypeError: replace() argument 2 must be str, not int
In [50]: s.replace("o", "O")
Out[50]: 'I lOve pythOn'
In [51]: s.replace("o", "O", -1)
Out[51]: 'I lOve pythOn'
In [52]: s.replace("o", "O", 0)
Out[52]: 'I love python'
In [53]: s.replace("o", "O", 1)
Out[53]: 'I lOve python'
In [54]: s.replace("o", "O", 5)
Out[54]: 'I lOve pythOn'str.strip()
str.rstrip()
str.lstrip()
移除 str 首尾指定字符汇合内的字符
In [62]: print(str.strip.__doc__)
S.strip([chars]) -> str
Return a copy of the string S with leading and trailing
whitespace removed.
If chars is given and not None, remove characters in chars instead.
In [66]: s = "I love python"
In [67]: s
Out[67]: 'I love python'
In [68]: s.strip() # 默认去掉首尾的空白字符
Out[68]: 'I love python'
In [69]: s.lstrip() # 去掉首部的空白字符
Out[69]: 'I love python'
In [70]: s.rstrip() # 去掉尾部的空白字符
Out[70]: 'I love python'
In [76]: s = "\n \r \t haha \n \r\t"
In [77]: s
Out[77]: '\n \r \t haha \n \r\t'
In [78]: s.strip()
Out[78]: 'haha'
In [84]: s = "I love python haha"
In [86]: s.strip("a")
Out[86]: 'I love python hah'
In [87]: s.strip("ha")
Out[87]: 'I love python'
In [88]: s.strip("on")
Out[88]: 'I love python haha'
In [89]: s
Out[89]: 'I love python haha'
In [91]: s = "{{haha haha}}"
In [92]: s
Out[92]: '{{haha haha}}'
In [94]: s.strip("{}")
Out[94]: 'haha haha'
In [95]: s.strip("{}s") # 移除指定字符汇合里的字符
Out[95]: 'haha haha'
In [96]: s.lstrip("{}s")
Out[96]: 'haha haha }}'str.ljust()
str.rjust()
左 \ 右对其并填充
In [98]: print(str.ljust.__doc__)
S.ljust(width[, fillchar]) -> str
Return S left-justified in a Unicode string of length width. Padding is
done using the specified fill character (default is a space).
In [105]: s = "xxj"
In [106]: s.ljust(3)
Out[106]: 'xxj'
In [107]: s.ljust(1)
Out[107]: 'xxj'
In [108]: s.ljust(10)
Out[108]: 'xxj'
In [109]: s.ljust(10, "A")
Out[109]: 'xxjAAAAAAA'
In [110]: s.ljust(10, "Ab")
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-110-b45e86b2e828> in <module>()
----> 1 s.ljust(10, "Ab")
TypeError: The fill character must be exactly one character long
In [111]: s.rjust(10, "A")
Out[111]: 'AAAAAAAxxj'5、查找
str.index()
str.rindex()
str.find()
str.rfind()
str.count()
In [32]: print(str.find.__doc__)
S.find(sub[, start[, end]]) -> int
Return the lowest index in S where substring sub is found,
such that sub is contained within S[start:end]. Optional
arguments start and end are interpreted as in slice notation.
Return -1 on failure.
In [23]: s = "I am xxj, i love python"
In [24]: s.find("x")
Out[24]: 5
In [25]: s.find("xx")
Out[25]: 5
In [26]: s.find("o")
Out[26]: 13
In [27]: s.find("o", 13, 13)
Out[27]: -1
In [28]: s.find("o", 13, 14)
Out[28]: 13
In [29]: s.find("o", 14, 50)
Out[29]: 21
In [30]: s.find("o", 14, 21)
Out[30]: -1
In [33]: s.find("A")
Out[33]: -1
In [34]: s.find("o", -1, -15)
Out[34]: -1
In [35]: s.find("o", -15, -1)
Out[35]: 13
In [37]: s.rfind("o")
Out[37]: 21str.index() 和 str.find() 的区别：
当给定的值不在查找范畴时，str.index() 会抛出 ValueError 而 str.find() 返回 -1
str 的 count() 办法和 list、tuple 的 count() 办法不一样，也能够限度查找范畴
str 有 rindex()，list、tuple 没有
6、判断
str.startswith()
str.endswith()
给定范畴内的 str 是否以给定 substr 结尾或结尾
In [64]: s
Out[64]: 'I am xxj, i love python'
In [66]: s.startswith("i")
Out[66]: False
In [67]: s.startswith("I")
Out[67]: True
In [68]: s.startswith("I am x")
Out[68]: True
In [69]: s.endswith("n")
Out[69]: True
In [70]: s.endswith("thon")
Out[70]: True
In [71]: s.startswith("x", 5)
Out[71]: True
In [72]: s.startswith("xxj", 5)
Out[72]: True
In [73]: s.startswith("xxj", 5, 5)
Out[73]: False
In [74]: s.startswith("xxj", 5, 7)
Out[74]: False
In [75]: s.startswith("xxj", 5, 8)
Out[75]: True7、isxxx() 判断类函数
看懂办法的意思就晓得用处
In [80]: s.isalnum()
Out[80]: False
In [81]: "abc123".isalnum()
Out[81]: True
In [82]: "abc123".isalpha()
Out[82]: False
In [83]: "abc".isalpha()
Out[83]: True
In [84]: "abc".isdecimal()
Out[84]: False
In [85]: "120".isdecimal()
Out[85]: True
In [86]: "120.123".isdecimal()
Out[86]: False
In [87]: "120.123".isdigit()
Out[87]: False
In [88]: "abc,".isdigit()
Out[88]: False
In [89]: ".,".isdigit()
Out[89]: False
In [90]: "120123".isdigit()
Out[90]: True
In [91]: "120123".isspace()
Out[91]: False
In [92]: "\t".isspace()
Out[92]: True