数据类型--字符串

字符串的定义

字符串或串(String)是由数字、字母、下划线组成的一串字符。它是编程语言中表示文本的数据类型。

一、 查看123和'123'的区别：

>>> a=123

>>> stra="123"
 
打印查看：结果显示一样
>>> print a
123

>>> print stra
123


 
交互式查看：区分引号
>>> a
123

>>> stra
'123'
 
显示类型查看：一个是数字，一个是字符
>>> type(a)
<type 'int'>

>>> type(stra)
<type 'str'>


计算2个变量发现：类型不匹配，字符串不能用于运算。 
>>> a+stra
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'

二、字符串的取值：

python字符串有2种取值顺序：

    从左到右索引默认0开始的，最大范围是字符串长度少1

    从右到左索引默认-1开始的，最大范围是字符串开头

 

列表中的值得分割，也可以用到变量[头下标:尾下标]，又称切片。
它可以截取相应的列表，从左到右索引默认0开始的，从右到左索引默认-1开始。
下标可以为空表示取到头或尾。

#!/usr/bin/python
s = 'ilovepython'
 print(s[1:5])

输出结果：
love。

 

三、字符串的换行：

注意：这么定义不能真实反映出数据的状态，如果不加 、缩进、空格那将会显得非常乱

>>> mail='tom:
 hello
 i am jack'
 
>>> mail
'tom:
 hello
 i am jack'
 
>>> print mail
tom:
hello
i am jack

四、定义字符串的方法：

使用三个引号作为字符串格式的定义

>>> mail="""tom:
 
...     i am jack
...     goodbye
... """
 
 
>>> print (mail)
tom:
    i am jack
    goodbye
 查看变量保存的格式：
 

>>> mail
'tom:
	i am jack
	goodbye
'

五、三个引号也可以作为注释

#!/usr/bin/python
"""input"""
a=int(raw_input("please input num1:"))
b=int(raw_input("please input num2:"))
print(a+b)
print(a-b)
print(a*b)
print(a/b)
 
显示结果：
[root@master1 pydata]# python 2.py
please input num1:3
please input num2:2
5
1
6
1

 

 

六、加号（+）是字符串连接运算符星号（*）是重复操作

str = 'Hello World!'

print(str) # 输出完整字符串
print(str[0]) # 输出字符串中的第一个字符
print(str[2:5]) # 输出字符串中第三个至第五个之间的字符串
print(str[2:]) # 输出从第三个字符开始的字符串
print(str * 2) # 输出字符串两次
print(str + "TEST") # 输出连接的字符串

Hello World!
H
llo
llo World!
Hello World!Hello World!
Hello World!TEST

字符串常用功能：

移除空白 ：print(str.split(" "))
分割：print(str.strip())
长度：　len(str)
索：  详情请看《数据类型--索引和切片》
切片：详情请看《数据类型--索引和切片》 

 

class str(basestring):
    """
    str(object='') -> string
    
    Return a nice string representation of the object.
    If the argument is a string, the return value is the same object.
    """
    def capitalize(self):  
        """ 首字母变大写 """
        """
        S.capitalize() -> string
        
        Return a copy of the string S with only its first character
        capitalized.
        """
        return ""

    def center(self, width, fillchar=None):  
        """ 内容居中，width：总长度；fillchar：空白处填充内容，默认无 """
        """
        S.center(width[, fillchar]) -> string
        
        Return S centered in a string of length width. Padding is
        done using the specified fill character (default is a space)
        """
        return ""

    def count(self, sub, start=None, end=None):  
        """ 子序列个数 """
        """
        S.count(sub[, start[, end]]) -> int
        
        Return the number of non-overlapping occurrences of substring sub in
        string S[start:end].  Optional arguments start and end are interpreted
        as in slice notation.
        """
        return 0

    def decode(self, encoding=None, errors=None):  
        """ 解码 """
        """
        S.decode([encoding[,errors]]) -> object
        
        Decodes S using the codec registered for encoding. encoding defaults
        to the default encoding. errors may be given to set a different error
        handling scheme. Default is 'strict' meaning that encoding errors raise
        a UnicodeDecodeError. Other possible values are 'ignore' and 'replace'
        as well as any other name registered with codecs.register_error that is
        able to handle UnicodeDecodeErrors.
        """
        return object()

    def encode(self, encoding=None, errors=None):  
        """ 编码，针对unicode """
        """
        S.encode([encoding[,errors]]) -> object
        
        Encodes S using the codec registered for encoding. encoding defaults
        to the default encoding. errors may be given to set a different error
        handling scheme. Default is 'strict' meaning that encoding errors raise
        a UnicodeEncodeError. Other possible values are 'ignore', 'replace' and
        'xmlcharrefreplace' as well as any other name registered with
        codecs.register_error that is able to handle UnicodeEncodeErrors.
        """
        return object()

    def endswith(self, suffix, start=None, end=None):  
        """ 是否以 xxx 结束 """
        """
        S.endswith(suffix[, start[, end]]) -> bool
        
        Return True if S ends with the specified suffix, False otherwise.
        With optional start, test S beginning at that position.
        With optional end, stop comparing S at that position.
        suffix can also be a tuple of strings to try.
        """
        return False

    def expandtabs(self, tabsize=None):  
        """ 将tab转换成空格，默认一个tab转换成8个空格 """
        """
        S.expandtabs([tabsize]) -> string
        
        Return a copy of S where all tab characters are expanded using spaces.
        If tabsize is not given, a tab size of 8 characters is assumed.
        """
        return ""

    def find(self, sub, start=None, end=None):  
        """ 寻找子序列位置，如果没找到，返回 -1 """
        """
        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.
        """
        return 0

    def format(*args, **kwargs): # known special case of str.format
        """ 字符串格式化，动态参数，将函数式编程时细说 """
        """
        S.format(*args, **kwargs) -> string
        
        Return a formatted version of S, using substitutions from args and kwargs.
        The substitutions are identified by braces ('{' and '}').
        """
        pass

    def index(self, sub, start=None, end=None):  
        """ 子序列位置，如果没找到，报错 """
        S.index(sub [,start [,end]]) -> int
        
        Like S.find() but raise ValueError when the substring is not found.
        """
        return 0

    def isalnum(self):  
        """ 是否是字母和数字 """
        """
        S.isalnum() -> bool
        
        Return True if all characters in S are alphanumeric
        and there is at least one character in S, False otherwise.
        """
        return False

    def isalpha(self):  
        """ 是否是字母 """
        """
        S.isalpha() -> bool
        
        Return True if all characters in S are alphabetic
        and there is at least one character in S, False otherwise.
        """
        return False

    def isdigit(self):  
        """ 是否是数字 """
        """
        S.isdigit() -> bool
        
        Return True if all characters in S are digits
        and there is at least one character in S, False otherwise.
        """
        return False

    def islower(self):  
        """ 是否小写 """
        """
        S.islower() -> bool
        
        Return True if all cased characters in S are lowercase and there is
        at least one cased character in S, False otherwise.
        """
        return False

    def isspace(self):  
        """
        S.isspace() -> bool
        
        Return True if all characters in S are whitespace
        and there is at least one character in S, False otherwise.
        """
        return False

    def istitle(self):  
        """
        S.istitle() -> bool
        
        Return True if S is a titlecased string and there is at least one
        character in S, i.e. uppercase characters may only follow uncased
        characters and lowercase characters only cased ones. Return False
        otherwise.
        """
        return False

    def isupper(self):  
        """
        S.isupper() -> bool
        
        Return True if all cased characters in S are uppercase and there is
        at least one cased character in S, False otherwise.
        """
        return False

    def join(self, iterable):  
        """ 连接 """
        """
        S.join(iterable) -> string
        
        Return a string which is the concatenation of the strings in the
        iterable.  The separator between elements is S.
        """
        return ""

    def ljust(self, width, fillchar=None):  
        """ 内容左对齐，右侧填充 """
        """
        S.ljust(width[, fillchar]) -> string
        
        Return S left-justified in a string of length width. Padding is
        done using the specified fill character (default is a space).
        """
        return ""

    def lower(self):  
        """ 变小写 """
        """
        S.lower() -> string
        
        Return a copy of the string S converted to lowercase.
        """
        return ""

    def lstrip(self, chars=None):  
        """ 移除左侧空白 """
        """
        S.lstrip([chars]) -> string or unicode
        
        Return a copy of the string S with leading whitespace removed.
        If chars is given and not None, remove characters in chars instead.
        If chars is unicode, S will be converted to unicode before stripping
        """
        return ""

    def partition(self, sep):  
        """ 分割，前，中，后三部分 """
        """
        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.
        """
        pass

    def replace(self, old, new, count=None):  
        """ 替换 """
        """
        S.replace(old, new[, count]) -> string
        
        Return a copy of string S with all occurrences of substring
        old replaced by new.  If the optional argument count is
        given, only the first count occurrences are replaced.
        """
        return ""

    def rfind(self, sub, start=None, end=None):  
        """
        S.rfind(sub [,start [,end]]) -> int
        
        Return the highest 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.
        """
        return 0

    def rindex(self, sub, start=None, end=None):  
        """
        S.rindex(sub [,start [,end]]) -> int
        
        Like S.rfind() but raise ValueError when the substring is not found.
        """
        return 0

    def rjust(self, width, fillchar=None):  
        """
        S.rjust(width[, fillchar]) -> string
        
        Return S right-justified in a string of length width. Padding is
        done using the specified fill character (default is a space)
        """
        return ""

    def rpartition(self, sep):  
        """
        S.rpartition(sep) -> (head, sep, tail)
        
        Search for the separator sep in S, starting at the end of S, and return
        the part before it, the separator itself, and the part after it.  If the
        separator is not found, return two empty strings and S.
        """
        pass

    def rsplit(self, sep=None, maxsplit=None):  
        """
        S.rsplit([sep [,maxsplit]]) -> list of strings
        
        Return a list of the words in the string S, using sep as the
        delimiter string, starting at the end of the string and working
        to the front.  If maxsplit is given, at most maxsplit splits are
        done. If sep is not specified or is None, any whitespace string
        is a separator.
        """
        return []

    def rstrip(self, chars=None):  
        """
        S.rstrip([chars]) -> string or unicode
        
        Return a copy of the string S with trailing whitespace removed.
        If chars is given and not None, remove characters in chars instead.
        If chars is unicode, S will be converted to unicode before stripping
        """
        return ""

    def split(self, sep=None, maxsplit=None):  
        """ 分割， maxsplit最多分割几次 """
        """
        S.split([sep [,maxsplit]]) -> list of strings
        
        Return a list of the words in the string 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.
        """
        return []

    def splitlines(self, keepends=False):  
        """ 根据换行分割 """
        """
        S.splitlines(keepends=False) -> 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.
        """
        return []

    def startswith(self, prefix, start=None, end=None):  
        """ 是否起始 """
        """
        S.startswith(prefix[, start[, end]]) -> bool
        
        Return True if S starts with the specified prefix, False otherwise.
        With optional start, test S beginning at that position.
        With optional end, stop comparing S at that position.
        prefix can also be a tuple of strings to try.
        """
        return False

    def strip(self, chars=None):  
        """ 移除两段空白 """
        """
        S.strip([chars]) -> string or unicode
        
        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.
        If chars is unicode, S will be converted to unicode before stripping
        """
        return ""

    def swapcase(self):  
        """ 大写变小写，小写变大写 """
        """
        S.swapcase() -> string
        
        Return a copy of the string S with uppercase characters
        converted to lowercase and vice versa.
        """
        return ""

    def title(self):  
        """
        S.title() -> string
        
        Return a titlecased version of S, i.e. words start with uppercase
        characters, all remaining cased characters have lowercase.
        """
        return ""

    def translate(self, table, deletechars=None):  
        """
        转换，需要先做一个对应表，最后一个表示删除字符集合
        intab = "aeiou"
        outtab = "12345"
        trantab = maketrans(intab, outtab)
        str = "this is string example....wow!!!"
        print str.translate(trantab, 'xm')
        """

        """
        S.translate(table [,deletechars]) -> string
        
        Return a copy of the string S, where all characters occurring
        in the optional argument deletechars are removed, and the
        remaining characters have been mapped through the given
        translation table, which must be a string of length 256 or None.
        If the table argument is None, no translation is applied and
        the operation simply removes the characters in deletechars.
        """
        return ""

    def upper(self):  
        """
        S.upper() -> string
        
        Return a copy of the string S converted to uppercase.
        """
        return ""

    def zfill(self, width):  
        """方法返回指定长度的字符串，原字符串右对齐，前面填充0。"""
        """
        S.zfill(width) -> string
        
        Pad a numeric string S with zeros on the left, to fill a field
        of the specified width.  The string S is never truncated.
        """
        return ""

    def _formatter_field_name_split(self, *args, **kwargs): # real signature unknown
        pass

    def _formatter_parser(self, *args, **kwargs): # real signature unknown
        pass

    def __add__(self, y):  
        """ x.__add__(y) <==> x+y """
        pass

    def __contains__(self, y):  
        """ x.__contains__(y) <==> y in x """
        pass

    def __eq__(self, y):  
        """ x.__eq__(y) <==> x==y """
        pass

    def __format__(self, format_spec):  
        """
        S.__format__(format_spec) -> string
        
        Return a formatted version of S as described by format_spec.
        """
        return ""

    def __getattribute__(self, name):  
        """ x.__getattribute__('name') <==> x.name """
        pass

    def __getitem__(self, y):  
        """ x.__getitem__(y) <==> x[y] """
        pass

    def __getnewargs__(self, *args, **kwargs): # real signature unknown
        pass

    def __getslice__(self, i, j):  
        """
        x.__getslice__(i, j) <==> x[i:j]
                   
                   Use of negative indices is not supported.
        """
        pass

    def __ge__(self, y):  
        """ x.__ge__(y) <==> x>=y """
        pass

    def __gt__(self, y):  
        """ x.__gt__(y) <==> x>y """
        pass

    def __hash__(self):  
        """ x.__hash__() <==> hash(x) """
        pass

    def __init__(self, string=''): # known special case of str.__init__
        """
        str(object='') -> string
        
        Return a nice string representation of the object.
        If the argument is a string, the return value is the same object.
        # (copied from class doc)
        """
        pass

    def __len__(self):  
        """ x.__len__() <==> len(x) """
        pass

    def __le__(self, y):  
        """ x.__le__(y) <==> x<=y """
        pass

    def __lt__(self, y):  
        """ x.__lt__(y) <==> x<y """
        pass

    def __mod__(self, y):  
        """ x.__mod__(y) <==> x%y """
        pass

    def __mul__(self, n):  
        """ x.__mul__(n) <==> x*n """
        pass

    @staticmethod # known case of __new__
    def __new__(S, *more):  
        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """
        pass

    def __ne__(self, y):  
        """ x.__ne__(y) <==> x!=y """
        pass

    def __repr__(self):  
        """ x.__repr__() <==> repr(x) """
        pass

    def __rmod__(self, y):  
        """ x.__rmod__(y) <==> y%x """
        pass

    def __rmul__(self, n):  
        """ x.__rmul__(n) <==> n*x """
        pass

    def __sizeof__(self):  
        """ S.__sizeof__() -> size of S in memory, in bytes """
        pass

    def __str__(self):  
        """ x.__str__() <==> str(x) """
        pass

字符串的练习

name = "my name is alex"

#首字母大写：
print(name.capitalize())

#判断变量是包含几个a
print(name.count("a"))

#左右填充，用“-”号代替
print(name.center(50,"-"))

#右填充，用“-”号代替
print("右填充",name.ljust(50,'-'))

#左填充，用“-”号代替
print("左填充",name.rjust(50,'-'))


#把字符串转成二进制：
a = name.encode()
print(a,type(a))

#判断一个字符串以什么为结尾
print(name.endswith("ex"))


#在	的位置打印多少个空格
text1 = "my name 	 is dongye"
print(text1.expandtabs())

#找到并取出字符的索引
print(name.find("e"))
print(name[name.find("name"):])    #可以用作切片

#格式化变量里面的字符串：
text2 = "my name  is {name} and i am {year} old"
print(text2.format(name='alix',year=23))


#同format用法一样：
text3 = "my name is {name} and i am {year} old"
print(text3.format_map({'name':'alex','year':12}))


#是否包含阿拉伯数字：
print(name.isalnum())
print('a1232'.isalnum())

#判断是否为整数
print(name.isdigit())
print("A1是否为整形：",'A1'.isdigit())
print("22是否为整形：",'22'.isdigit())


#判断是不是一个合法的标识符
print('a A1'.isidentifier())

#判断是否为
print("判断a是否为小写：",'a'.islower())


#判断是否为大写：
print("判断是否为大写:",'DONGYE'.isupper())


#把大写转为小写：
print("大写转小写："'Alex'.lower())

#把小写转为大写：
print("小写转大写："'Alex'.upper())


#判断是否为空格：
print("判读是否为空格",' '.isnumeric())


#判断每个字符首字母是否为大写：
print("每个字符串首字母是否为大写：",'My Name Is '.istitle())


#字符串间加特殊符号、字符、表达式
print('+'.join(['a','b','c','d']))


#去掉左面的回车和空格
print("去掉左面的回车和空格：",'
Alex'.lstrip())

#去掉右面面的回车和空格
print("去掉右面的回车和空格：",'Alex
'.rstrip())
print("---")


#去掉左右两边的回车和空格：
print("去掉右面的回车和空格：",'
Alex
'.strip())


#可以当做随机密码：
p = str.maketrans("abcdef",'123456')
print("alexli".translate(p))


#替换所有和单个字符：
#replace('源字符','替换字符',第几个)
print("所有小写l替换成大写L：",'alex li'.replace('l','L'))
print("所有小写l替换成大写L：",'aieix li ding lei'.replace('i','L',3))

#查找最后一个指定值的下标：
print("从左往右数找到最后一个'l'下标",'alex lil'.rfind('l'))


#去掉or按照指定字符分割成列表：
print("字符串按照指定字符分割成列表：",'alex li'.split( ))
print("字符串按照指定字符分割成列表：",'a+2+3+4'.split('+'))  #常用
print("字符串按照指定字符分割成列表：",'a+2+3+4'.split('
'))
print("字符串按照指定字符分割成列表：",'a+2
+3+4'.splitlines()) #识别不同系统的换行。

#判断以什么为开头：
print('AlexLi'.startswith('A'))

#大写变小写，小写变大写：
print('AlexLi'.swapcase())


#每个字符首字母改成大写：
print('al ex li'.title())