python--字符串

字符串是 Python 中最常用的数据类型。我们可以使用引号('或")来创建字符串。

# eg_v1
var1 = "hello,welcome to python~"
print (var1)
print (type(var1))

注:标准的序列操作(索引,分片,乘法,判断成员资格,求长度,取最大值和最小值)对字符串也是适用的.但字符串是不可变的,分片赋值不合法.

1.字符串格式化

注:如果需要转换的元组作为转换表达式的一部分存在,必须将它用圆括号括起来

格式化符号说明

# 格式化符号	说明
# %c	        转换成字符(ASCII 码值,或者长度为一的字符串)
# %r	        优先用repr()函数进行字符串转换(Python2.0新增)
# %s	        优先用str()函数进行字符串转换
# %d / %i	    转成有符号十进制数
# %u	        转成无符号十进制数
# %o	        转成无符号八进制数
# %x / %X	    (Unsigned)转成无符号十六进制数(x / X 代表转换后的十六进制字符的大小写)
# %e / %E	    转成科学计数法(e / E控制输出e / E)
# %f / %F	    转成浮点数(小数部分自然截断)
# %g / %G	%e和%f / %E和%F 的简写
# %%	        输出%

  

2. 简单转换

# eg_v2
print ("price of eggs: $%d" % 42)
print ("Hexadecimal price of eggs: %x" % 42)

3. 字段宽带和精度

字段宽度 是转换后的值保留最小字符个数

精度 是结果中包含的小数位数

#eg_v3
from math import pi
print ("%10f " % pi)   #  字宽度为10
print ("%10.2f" %pi)  # 字段宽 10,精度2
print ("%.2f" % pi)   # 精度 2
4. 符号、对齐 和 0 填充

在字段宽度和精度值之前可以放置一个“标表”,该标表可以为零,加号,减号或空格。零表示数字将会用0填充

字符串格式化实例

name = input("input your name:")
age = int(input("input your age:"))
job = input("input your job:")

msg = '''
information of user of %s:
-------------------------
Nane:   %s
Age:    %d
Job:    %s
--------End--------------
''' %(name,name,age,job)
print (msg)

# %s 代表字符串格式
# %d 代表整数格式
# %f 代表浮点数格式

  

字符串方法

1. find

find 方法可以在一个较长的字符串中查找子字符串。

moo = "with a moo-moo here.and a moo-moo there."
print (moo.find("moo"))
# # 7
tittle = "monty python's flying circus"
print (tittle.find("python"))
# 6

  

字符串操作方法

字符串可以使用双引号或单引号来表示开始和结束,。使用双引号的一个好处,就是字符串中可以使用单引号字符

字符串转义字符

转义字符	含义
\(在行尾时)	续行符
\\	反斜杠符号
\'	单引号
\"	双引号
\a	响铃
\b	退格(Backspace)
\e	转义
\000	空
\n	换行
\v	纵向制表符
\t	横向制表符
\r	回车
\f	换页
\oyy	八进制数,yy代表的字符,例如:\o12代表换行
\xyy	十六进制数,yy代表的字符,例如:\x0a代表换行
\other	其它的字符以普通格式输出

  

原始字符串
在字符串开始的引号之前加上r,使它成为原始字符串。“原始字符串”完全忽略所有的转义字符,打印出字符串中所有的倒斜杠

print (r"hello,welvome to python\n,and\r")
# hello,welvome to python\n,and\r



字符串下标和切片
字符串像列表一样,使用下标和切片

L = "WelcomeToPython"
print (L[0])
print (L[4])
print (L[-1])
print (L[0:5])
print (L[:5])
print (L[6:0])
# W
# o
# n
# Welco
# Welco

  

字符串的in 和not in 操作符
像列表一样,in 和not in 操作符也可以用于字符串。用in 或not in 连接两个字符串得到的表达式,将求值为布尔值True 或False

L = "Welcome To Python"
print ("To" in L)
print ("And" in L)
print ("Python" not in L)
# True
# False
# False

  

字符串方法upper()、lower()、isupper()和islower()
upper()字符串方法返回一个新字符串,其中原字符串的所有字母都被相应地转换为大写
lower()字符串方法返回一个新字符串,其中原字符串的所有字母都被相应地转换为小写

L = "Welcome To Python"
l1 = L.upper()
print (l1)
# WELCOME TO PYTHON
l2 = L.lower()
print (l2)
# welcome to python

  



如果字符串至少有一个字母,并且所有字母都是大写或小写,isupper()和islower()方法就会相应地返回布尔值True。否则,该方法返回False

l3 = l1.isupper()
print (l3)
# True
l4 = l2.islower()
print (l4)
# True

  

isX 字符串方法

 isalpha()返回True,如果字符串只包含字母,并且非空;
 isalnum()返回True,如果字符串只包含字母和数字,并且非空;
 isdecimal()返回True,如果字符串只包含数字字符,并且非空;
 isspace()返回True,如果字符串只包含空格、制表符和换行,并且非空;
 istitle()返回True,如果字符串仅包含以大写字母开头、后面都是小写字母的单词。

  

字符串方法startswith()和endswith()
startswith()和endswith()方法返回True,如果它们所调用的字符串以该方法传入的字符串开始或结束。否则,方法返回False

print ('Hello world!'.startswith('Hello'))
# True
print ('Hello world!'.endswith('world!'))
# True

  

字符串方法join()和split()
join()方法在一个字符串上调用,参数是一个字符串列表,返回一个字符串。返回的字符串由传入的列表中每个字符串连接而成

LIST1 = ["A","B","C","D","E","F"]
print ("+".join(LIST1))
# A+B+C+D+E+F

split()用法,是按照换行符分割多行字符串

LIST2 = "A+B+C+D+E+F"
print (LIST2.split("+"))
# ['A', 'B', 'C', 'D', 'E', 'F']

  

用rjust()、ljust()和center()方法对齐文本
rjust()和ljust()字符串方法返回调用它们的字符串的填充版本,通过插入空格来对齐文本。这两个方法的第一个参数是一个整数长度,用于对齐字符串

print ("Python".rjust(10)) # 右对齐
# Python
print ("Python".ljust(10)) # 左对齐
# Python 
print ("Python".center(10)) # 居中
# Python  

  

用strip()、rstrip()和lstrip()删除空白字符
删除字符串左边、右边或两边的空白字符(空格、制表符和换行符)。strip()字符串方法将返回一个新的字符串,它的开头或末尾都没有空白字符。
lstrip()和rstrip()方法将相应删除左边或右边的空白字符。

LIST3 = " Welcome To Python "
print (LIST3.strip())
# Welcome To Python
print (LIST3.rstrip())
# Welcome To Python
print (LIST3.lstrip())
# Welcome To Python 

有一个可选的字符串参数,指定两边的哪些字符应该删除

LIST4 = "AABBCCDDEEFFAA"
print (LIST4.strip("AA"))
# BBCCDDEEFF
print (LIST4.strip("BB")) # 注:如果不是两边的,无法删除,还是返回原字符串
# AABBCCDDEEFFAA

  

translate,replace

translate 与replace一样,替换字符串的某些部分.但translate只处理单个字符,并且可以同时进行多个替换

字符串官方文档解析

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__
        """
        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__
        """
        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__
        """
        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 ""

  

posted @ 2017-03-07 17:59  xie仗剑天涯  阅读(429)  评论(0编辑  收藏  举报