python string

如果这就是字符串，这本来就是字符串

首先看下字符串的方法

>>> dir(str)
['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_formatter_field_name_split', '_formatter_parser', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

lower(...)
    Return a copy of the string s converted to lowercase.
    将字符串中大写字母转换为小写
 
upper(...)
    Return a copy of the string s converted to uppercase. 
    将字符串中小写字母转换为大写

swapcase(...)
    Return a copy of the string s with upper case characters
    converted to lowercase and vice versa.
    将字符串中的字母互换大小写

strip(...)
    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
    移出字符串首尾的空格
lstrip(...)
    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
    移出字符串首部的空格
rstrip(...)
    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
    移出字符串尾部的空格

split(...)
    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.
    分割字符串，如果给定了分隔符，按照分隔符号分割，否则按照空格进行分割。
    如果指定了最大分割次数，则按照最大分割次数分割，否则分割所有。

rsplit(...)
    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.
    同split作用一样，但是是从尾部开始进行分割。

join(...)
    S.join(iterable) -> string
   
    Return a string which is the concatenation of the strings in the
    iterable.  The separator between elements is S.
    方法中传递的参数是一个iterable，然后在元素之间加入分隔符串联成一个字符串返回。

startswith(...)
    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.
    判断一个字符串的开始

endswith(...)
    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.
    判断一个字符串的结尾

count(...)
    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.
    计算指定子字符串sub的出现次数

find(...)
    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.
    找到指定子字符串sub首次出现的位置，否则返回-1

rfind(...)
    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.
    找到一个子字符串最后一次出现的位置

index(...)
    S.index(sub [,start [,end]]) -> int
   
    Like S.find() but raise ValueError when the substring is not found.
    找到指定子字符串sub首次出现的位置，否则报错。

rindex(...)
    S.rindex(sub [,start [,end]]) -> int
   
    Like S.rfind() but raise ValueError when the substring is not found.
    找到指定子字符串sub最后一次出现的位置，否则报错。

ljust(...)
    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).
    >>> s='abcde'
    >>> s.ljust(10)
    'abcde     '

rjust(...)
    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)
    在长度为width的字符串内向右对齐。
    >>> s='abcde'
    >>> s.rjust(10)
    '     abcde'

partition(...)
    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.
    使用分隔符字符串sep划分字符串，返回一个元组。
    >>> s='abcde'
    >>> s.partition('c')
    ('ab', 'c', 'de')

rpartition(...)
    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.
    使用分隔符字符串sep划分字符串，但是从字符串的结尾处开始搜索。

encode(...)
    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.
    返回字符串的编码版本

decode(...)
    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.
    解码一个字符串并返回一个Unicode字符串，

capitalize(...)
    S.capitalize() -> string
   
    Return a copy of the string S with only its first character
    capitalized.center
    首字符变成大写
center(...)
    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)
    在长度为width的字段内将字符串居中。pad是填充字符。
expandtabs(...)
    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.
    使用空格替换制表符    

format(...)
    S.format(*args, **kwargs) -> string
   
    Return a formatted version of S, using substitutions from args and kwargs.
    The substitutions are identified by braces ('{' and '}').
    格式化

replace(...)
    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.
    替换一个子字符串

translate(...)
    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.
    使用一个字符转换表table转换字符串，删除deletechars中的字符

splitlines(...)
    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.
    将字符串分为一个行列表，如果keepends为1，则保留各行最后的换行符。

title(...)
    S.title() -> string
   
    Return a titlecased version of S, i.e. words start with uppercase
    characters, all remaining cased characters have lowercase.
    将字符串转换为标题格式
    s='hello,word'
    s.title()
    输出：'Hello,World'

zfill(...)
    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.
    在字符串的左边填充0，直至其宽度为width

isalnum
    检查所有字符是否都为字母或数字
isalpha
    检查所有字符是否都为字母
isdigit
    检查所有字符是否都为数字
islower
    检查所有字符是否都为小写
isspace
    检查所有字符是否都为空白
istitle
    检查所有字符是否为标题字符串
isupper
    检查所有字符是否为大写

Q：

1、给定字符串 s='simple is better' 统计字符串中字符出现的次数，并且按照次数排序。

def f_1(s):
    counter = {}
    for i in s:
        if not counter.has_key(i):
            counter[i] = s.count(i)
        else:
            continue
    return sorted(counter.items(), key=lambda d: d[1],reverse=True)

2、给定一个list，转换为字符串。list=['d','o','n','e']转换为字符串'done'.

def f(l):
     return ''.join(l)

参考资料：
http://docs.python.org/2/library/string.html