python开发【二】python基本数据类型之字符串

一、运算符

1、算法运算符

 

2、比较运算

 

3、赋值运算

4、逻辑运算

5、成员运算

 

 二、基本数据类型之字符串

1、数字 int

int(整型) 在python3中数字不在区分整型与长整型，都叫做整型。

数字方法：

 int 整型转换

a = '1234'
b = int(b)  #把字符串‘1234’转换成1234

int禁止转换

int(number,16)

a = '1011'
b = int(a)     #默认转换成十进制
print('b=',b)
c = int(a,2)   #把二进制格式转换成十进制
print('c=',c)

 

输出结果：

b= 1011
c= 11

2、布尔值 bool

　　真或假

　　1 或 0

3、字符串 str

a = 'abcdabcdabcd'

 

字符串常用功能：

class str(object):
    """
    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'.
    """
    def capitalize(self): # real signature unknown; restored from __doc__
        """ """首字母变大写"""

        S.capitalize() -> str
        
        Return a capitalized version of S, i.e. make the first character
        have upper case and the rest lower case.
        """
        return ""

    def casefold(self): # real signature unknown; restored from __doc__
        """ """所有字母变小写"""
        S.casefold() -> str
        
        Return a version of S suitable for caseless comparisons.
        """
        return ""

    def center(self, width, fillchar=None): # real signature unknown; restored from __doc__
        """ 内容居中， width：总长度；fillchar:空白处填充内容，默认无(可以指定填充字符) """
　　　　 """　

        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)
        """
        return ""

    def count(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
        """
        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 encode(self, encoding='utf-8', errors='strict'): # real signature unknown; restored from __doc__
        """
        S.encode(encoding='utf-8', errors='strict') -> bytes
        
        Encode S using the codec registered for encoding. Default encoding
        is 'utf-8'. 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 can handle UnicodeEncodeErrors.
        """
        return b""

    def endswith(self, suffix, start=None, end=None): # real signature unknown; restored from __doc__
        """
        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=8): # real signature unknown; restored from __doc__
        """
        S.expandtabs(tabsize=8) -> str
        
        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): # real signature unknown; restored from __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.
        """
        return 0

    def format(self, *args, **kwargs): # known special case of str.format
        """
        S.format(*args, **kwargs) -> str
        
        Return a formatted version of S, using substitutions from args and kwargs.
        The substitutions are identified by braces ('{' and '}').
        """
        pass

    def format_map(self, mapping): # real signature unknown; restored from __doc__
        """
        S.format_map(mapping) -> str
        
        Return a formatted version of S, using substitutions from mapping.
        The substitutions are identified by braces ('{' and '}').
        """
        return ""

    def index(self, sub, start=None, end=None): # real signature unknown; restored from __doc__
        """
        S.index(sub[, start[, end]]) -> int
        
        Like S.find() but raise ValueError when the substring is not found.
        """
        return 0

    def isalnum(self): # real signature unknown; restored from __doc__
        """
        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): # real signature unknown; restored from __doc__
        """
        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 isdecimal(self): # real signature unknown; restored from __doc__
        """
        S.isdecimal() -> bool
        
        Return True if there are only decimal characters in S,
        False otherwise.
        """
        return False

    def isdigit(self): # real signature unknown; restored from __doc__
        """
        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 isidentifier(self): # real signature unknown; restored from __doc__
        """
        S.isidentifier() -> bool
        
        Return True if S is a valid identifier according
        to the language definition.
        
        Use keyword.iskeyword() to test for reserved identifiers
        such as "def" and "class".
        """
        return False

    def islower(self): # real signature unknown; restored from __doc__
        """
        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 isnumeric(self): # real signature unknown; restored from __doc__
        """
        S.isnumeric() -> bool
        
        Return True if there are only numeric characters in S,
        False otherwise.
        """
        return False

    def isprintable(self): # real signature unknown; restored from __doc__
        """
        S.isprintable() -> bool
        
        Return True if all characters in S are considered
        printable in repr() or S is empty, False otherwise.
        """
        return False

    def isspace(self): # real signature unknown; restored from __doc__
        """
        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): # real signature unknown; restored from __doc__
        """
        S.istitle() -> bool
        
        Return True if S is a titlecased string and there is at least one
        character in S, i.e. upper- and titlecase characters may only
        follow uncased characters and lowercase characters only cased ones.
        Return False otherwise.
        """
        return False

    def isupper(self): # real signature unknown; restored from __doc__
        """
        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): # real signature unknown; restored from __doc__
        """
        S.join(iterable) -> str
        
        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): # real signature unknown; restored from __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).
        """
        return ""

    def lower(self): # real signature unknown; restored from __doc__
        """
        S.lower() -> str
        
        Return a copy of the string S converted to lowercase.
        """
        return ""

    def lstrip(self, chars=None): # real signature unknown; restored from __doc__
        """
        S.lstrip([chars]) -> str
        
        Return a copy of the string S with leading whitespace removed.
        If chars is given and not None, remove characters in chars instead.
        """
        return ""

    def maketrans(self, *args, **kwargs): # real signature unknown
        """
        Return a translation table usable for str.translate().
        
        If there is only one argument, it must be a dictionary mapping Unicode
        ordinals (integers) or characters to Unicode ordinals, strings or None.
        Character keys will be then converted to ordinals.
        If there are two arguments, they must be strings of equal length, and
        in the resulting dictionary, each character in x will be mapped to the
        character at the same position in y. If there is a third argument, it
        must be a string, whose characters will be mapped to None in the result.
        """
        pass

    def partition(self, sep): # real signature unknown; restored from __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.
        """
        pass

    def replace(self, old, new, count=None): # real signature unknown; restored from __doc__
        """
        S.replace(old, new[, count]) -> str
        
        Return a copy of 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): # real signature unknown; restored from __doc__
        """
        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): # real signature unknown; restored from __doc__
        """
        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): # real signature unknown; restored from __doc__
        """
        S.rjust(width[, fillchar]) -> str
        
        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): # real signature unknown; restored from __doc__
        """
        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=-1): # real signature unknown; restored from __doc__
        """
        S.rsplit(sep=None, maxsplit=-1) -> list of strings
        
        Return a list of the words in 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, any whitespace string
        is a separator.
        """
        return []

    def rstrip(self, chars=None): # real signature unknown; restored from __doc__
        """
        S.rstrip([chars]) -> str
        
        Return a copy of the string S with trailing whitespace removed.
        If chars is given and not None, remove characters in chars instead.
        """
        return ""

    def split(self, sep=None, maxsplit=-1): # real signature unknown; restored from __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.
        """
        return []

    def splitlines(self, keepends=None): # real signature unknown; restored from __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.
        """
        return []

    def startswith(self, prefix, start=None, end=None): # real signature unknown; restored from __doc__
        """
        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): # real signature unknown; restored from __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.
        """
        return ""

    def swapcase(self): # real signature unknown; restored from __doc__
        """
        S.swapcase() -> str
        
        Return a copy of S with uppercase characters converted to lowercase
        and vice versa.
        """
        return ""

    def title(self): # real signature unknown; restored from __doc__
        """
        S.title() -> str
        
        Return a titlecased version of S, i.e. words start with title case
        characters, all remaining cased characters have lower case.
        """
        return ""

    def translate(self, table): # real signature unknown; restored from __doc__
        """
        S.translate(table) -> str
        
        Return a copy of the string S in which each character has been mapped
        through the given translation table. The table must implement
        lookup/indexing via __getitem__, for instance a dictionary or list,
        mapping Unicode ordinals to Unicode ordinals, strings, or None. If
        this operation raises LookupError, the character is left untouched.
        Characters mapped to None are deleted.
        """
        return ""

    def upper(self): # real signature unknown; restored from __doc__
        """
        S.upper() -> str
        
        Return a copy of S converted to uppercase.
        """
        return ""

    def zfill(self, width): # real signature unknown; restored from __doc__
        """
        S.zfill(width) -> str
        
        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 __add__(self, *args, **kwargs): # real signature unknown
        """ Return self+value. """
        pass

    def __contains__(self, *args, **kwargs): # real signature unknown
        """ Return key in self. """
        pass

    def __eq__(self, *args, **kwargs): # real signature unknown
        """ Return self==value. """
        pass

    def __format__(self, format_spec): # real signature unknown; restored from __doc__
        """
        S.__format__(format_spec) -> str
        
        Return a formatted version of S as described by format_spec.
        """
        return ""

    def __getattribute__(self, *args, **kwargs): # real signature unknown
        """ Return getattr(self, name). """
        pass

    def __getitem__(self, *args, **kwargs): # real signature unknown
        """ Return self[key]. """
        pass

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

    def __ge__(self, *args, **kwargs): # real signature unknown
        """ Return self>=value. """
        pass

    def __gt__(self, *args, **kwargs): # real signature unknown
        """ Return self>value. """
        pass

    def __hash__(self, *args, **kwargs): # real signature unknown
        """ Return hash(self). """
        pass

    def __init__(self, value='', encoding=None, errors='strict'): # known special case of str.__init__
        """
        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'.
        # (copied from class doc)
        """
        pass

    def __iter__(self, *args, **kwargs): # real signature unknown
        """ Implement iter(self). """
        pass

    def __len__(self, *args, **kwargs): # real signature unknown
        """ Return len(self). """
        pass

    def __le__(self, *args, **kwargs): # real signature unknown
        """ Return self<=value. """
        pass

    def __lt__(self, *args, **kwargs): # real signature unknown
        """ Return self<value. """
        pass

    def __mod__(self, *args, **kwargs): # real signature unknown
        """ Return self%value. """
        pass

    def __mul__(self, *args, **kwargs): # real signature unknown
        """ Return self*value.n """
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __ne__(self, *args, **kwargs): # real signature unknown
        """ Return self!=value. """
        pass

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    def __rmod__(self, *args, **kwargs): # real signature unknown
        """ Return value%self. """
        pass

    def __rmul__(self, *args, **kwargs): # real signature unknown
        """ Return self*value. """
        pass

    def __sizeof__(self): # real signature unknown; restored from __doc__
        """ S.__sizeof__() -> size of S in memory, in bytes """
        pass

    def __str__(self, *args, **kwargs): # real signature unknown
        """ Return str(self). """
        pass

附录：

 

字符串方法示例：

1. 首字母大写 capitalize()

a = 'joechu'
print(a.capitalize())
输出：
Joechu

2.所有字母转换成小写[通用方法] lower()

a = 'joeCHU'
v = a.lower()
print(v)
输出：
joechu

3.所有字母转换成小写[通lower增强版] casefold()

a = 'joeCHU'
v = a.casefold()
print(v)
输出:
joechu

4.所有字母转换成大写 uppper()

a = 'abcdEf'
b = a.upper()
print(b)
输出：
ABCDEF

5. 设置宽度，并将内容居中 ，默认以空白填充 center(width，'填充符号')

a = 'joeCHU'
v = a.center(20)
print(v)
输出：
       joeCHU                 #空白认处填充内容，默认无

v1 = a.center(20,'-')     #空白处指定用‘-’填充
print(v1)
输出：
-------joeCHU-------

6. 设置宽度，内容居左

a = 'joecHUjoechue'
v1 = a.ljust(20)
v2 = a.ljust(20,"*")
print(v1)
print(v2)
输出：
joecHUjoechue       
joecHUjoechue*******

7. 设置宽度，内容居右

a = 'joecHUjoechue'
v1 = a.rjust(20)
v2 = a.rjust(20,"*")
print(v1)
print(v2)
输出：
       joecHUjoechue
*******joecHUjoechue　

8.计算字符出现的次数 count(‘str’) 

a = 'joecHUjoechue'

v = a.count('e')
print(v)
输出：
3
v1 = a.count('e',3,10)    #指定第3个字符开始，第10个字符结束之间出现e的次数
print(v1)
输出：
1

9.应某某字符结尾，可以指定区间，正确返回True，反之False    endswith('str',start,end)；startswith('str',start,end)用法跟endswith类似。

a = 'joecHUjoechue'
v = a.endswith('ue')
print(v)
v1 = a.endswith('u')
print(v1)
v2 = a.endswith('u',2,12)
print(v2)
输出：
True         #v1返回值
False        #v2返回值
True         #v3返回值

10.已xxx开始

a = 'joecHUjoechue'
v = a.startswith('jo')
print(v)
v1 = a.startswith('o')
print(v1)
v2 = a.startswith('ec',2,12)
print(v2)
输出：
True
False
True

11.从开始往后查找字符串，当找到第一个字符串时，获取字符串下标并停止。

a = 'joecHUjoechue'
v = a.find('o')
print(v)
v2 = a.find('U')
print(v2)
输出：
1        #v输出
5        #v2输出
v3 = a.find('o',2,8)    #指定查找区间
print(v3)
输出：
7

12. 从右边查找sub，如果查到第一个返回索引值，不存在返回-1,可以指定查找范围

a = 'iuoecHUjoecxui'
v = a.rfind('x')
print(v)
v2 = a.rfind('i')
print(v2)
输出：
11
13

13.获取位置下标index()，如果字符串不存在，报错  

a = 'cxfjoe'
v1 = a.index('x')
print(v1)
输出：
1

当字符串不存在时，会在执行后直接报错

a = 'cxfjoe'
v2 = a.index('m')
print(v2)
输出：
  File "D:/Python_Projiect/2test.py", line 2, in <module>
    v2 = a.index('m')
ValueError: substring not found

14.判断字符串是否只包含字母和数字 isalnum()

a = 'cxfjoe'
v = a.isalnum()
print(v)
输出:
True
###############
a1 = 'cxfjoe123'
v1 = a.isalnum()
print(v1)
输出：
True
###############
a2 = 'cxfjoe123@'
v2 = a2.isalnum()
print(v2)
输出：
False
###############
a3 = '123'
v3 = a3.isalnum()
print(v3)
输出：
True

15.判断是否只包含字母 isalpha()

a = 'Abcadfd'
b = 'abcd@12'
v1 = a.isalnum()
v2 = b.isalnum()
print(v1)
print(v2)
输出：
True
False

16.判断字符串是否只包含数字 isdigit()

a = '1223'
b = 'abcd@12'
v1 = a.isalnum()
v2 = b.isalnum()
print(v1)
print(v2)
输出：
True
False

 

17. expandtabs() 制表符断句

s = '1234561ea\tabcded\tdss'
v = s.expandtabs(6)
print(v)
输出：
1234561ea   abcded      dsse

expandtabs解释：

expandtabs制作表格

name = 'username\temail\tpassword\njoe\t123@163.com\t123\nxiaoyong\t456@163.com\t456'
v = name.expandtabs(20)
print(v)
输出：
username             email                   password
joe                  123@163.com             123
xiaoyong             456@163.com             456

18. 格式化 format

a = 'c{}x{}f{}x'
v = a.format('A','B','D')
print(v)
输出：
cAxBfDx

 字符串的7个基本魔法：

join        指定字符串拼接

split        分割

strip        移除空格

upper      转换大写

lower      转换小写

replace   替换

字符串的4个灰魔法：

1. for 循环

2.索引  下标

3.切片

4.获取长度(len)

三、字符串练习

1. 方法链

方法链的作用：从一个方法返回的对象可以用做另一种方法中的主调对象。

a = 'welcome to Python'
v1 = a.upper()
print(v1)
v2 = a.upper().find("E")       #方法链
print(v2)
输出：
WELCOME TO PYTHON
1　

1.1 可选参数

a = 'welcome to Python'
v1 = a.upper().find("W")
v2 = a.upper().find("L")
v3 = a.upper().find("E",2,4)     #可选参数，指定查找范围
print(v1)
print(v2)
print(v3)
输出：
0         #下标
2         #下标
-1        #不存在，返回-1

2.方法嵌套

查找第二次w的索引下标

a = 'welcometopythonwelcomewelcome'
v1 = a.find('w',a.find('w')+1)                     #嵌套
print(v1)
输出：
15

3.字符串与控制语句

a = 'welcometopython'
for i in a:
    print(i)
输出：
w
e
l
c
o
m
e
t
o
p
y
t
h
o
n

在python3中，默认print(i,end='\n'）

不想换行 print(i,end = ' ')

a = 'welcometopython'
for i in a:
    print(i,end = ' ')              #指定空格
输出：
w e l c o m e t o p y t h o n 

获取字符串下标：

a = 'welcometopython'
for index in range(len(a)):
    print(index,end = ' ')
输出：
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

 通过下标获取字符串元素：

a = 'welcometopython'
for index in range(len(a)):
    print(a[index],end = ' ')
输出：
w e l c o m e t o p y t h o n 

enumerate迭代器   

将一个可遍历的数据对象(如列表、元组或字符串)组合为一个索引序列，同时列出数据和数据下标

a = 'welcome'
for index,letter in enumerate(a):
    print(index,letter)
输出：
0 w
1 e
2 l
3 c
4 o
5 m
6 e

 获取元组1

a = 'welcome'
for value in enumerate(a):
    print(value)
输出：
(0, 'w')
(1, 'e')
(2, 'l')
(3, 'c')
(4, 'o')
(5, 'm')
(6, 'e')