6.python字元串-內置方法列舉

　　所謂內置方法，就是凡是字元串都能用的方法，這個方法在創建字元串的類中，下麵是總結：

　　首先，我們要學習一個獲取幫助的內置函數 help(對象) ，對象可以是一個我們創建出來的，也可以是創建對象的那個類，類也是一個對象，被稱為類對象。

　　當我們進入解釋器的交互模式中輸入以下代碼時：

help(str)

　　其中，str就是創建字元串的類，然後我們就會得到一長串的結果：

Help on class str in module __builtin__:

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.
 |  
 |  Method resolution order:
 |      str
 |      basestring
 |      object
 |  
 |  Methods defined here:
 |  
 |  __add__(...)
 |      x.__add__(y) <==> x+y　　#字元串拼接，看+號就知道
 |  
 |  __contains__(...)
 |      x.__contains__(y) <==> y in x　　#判斷x里字元是否在y里
 |  
 |  __eq__(...)
 |      x.__eq__(y) <==> x==y　　
 |  
 |  __format__(...)
 |      S.__format__(format_spec) -> string
 |      
 |      Return a formatted version of S as described by format_spec.
 | 
 |  __ge__(...)
 |      x.__ge__(y) <==> x>=y
 |  
 |  __getattribute__(...)
 |      x.__getattribute__('name') <==> x.name　　#獲取屬性
 |  
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]　　#索引取值，詳情參考python中的序列
 |  
 |  __getnewargs__(...)
 |  
 |  __getslice__(...)
 |      x.__getslice__(i, j) <==> x[i:j]　　#切片，也是序列的一種方法
 |      
 |      Use of negative indices is not supported.
 |  
 |  __gt__(...)
 |      x.__gt__(y) <==> x>y
 |  
 |  __hash__(...)
 |      x.__hash__() <==> hash(x)　　
 |  
 |  __le__(...)
 |      x.__le__(y) <==> x<=y
 |  
 |  __len__(...)
 |      x.__len__() <==> len(x)
 |  
 |  __lt__(...)
 |      x.__lt__(y) <==> x<y
 |  
 |  __mod__(...)
 |      x.__mod__(y) <==> x%y
 |  
 |  __mul__(...)
 |      x.__mul__(n) <==> x*n
 |  
 |  __ne__(...)
 |      x.__ne__(y) <==> x!=y
 |  
 |  __repr__(...)
 |      x.__repr__() <==> repr(x)
 |  
 |  __rmod__(...)
 |      x.__rmod__(y) <==> y%x
 |  
 |  __rmul__(...)
 |      x.__rmul__(n) <==> n*x
 |  
 |  __sizeof__(...)
 |      S.__sizeof__() -> size of S in memory, in bytes　　#用位元組表示在記憶體中的大小
 |  
 |  __str__(...)
 |      x.__str__() <==> str(x)
 |  
 |  capitalize(...)
 |      S.capitalize() -> string
 |      '''返迴首字母大寫字元串副本,對中文無效'''
 |      Return a copy of the string S with only its first character
 |      capitalized.
 |  
 |  center(...)
 |      S.center(width[, fillchar]) -> string
 |      '''返回指定寬度（width）的字元串副本，原字元串居中對齊，可指定用什麼來填充多餘部分（fillchar）預設為空格，關於對齊和填充可以看上篇博文的解釋'''
 |      Return S centered in a string of length width. Padding is
 |      done using the specified fill character (default is a space)
 |  
 |  count(...)
 |      S.count(sub[, start[, end]]) -> int
 |      '''計數器，返回給定字元串在原字元串出現的次數，也可指定範圍'''
 |      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.
 |  
 |  decode(...)
 |      S.decode([encoding[,errors]]) -> object
 |      '''解碼，將字元串解碼成某種字元集'''
 |      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.
 |  
 |  encode(...)
 |      S.encode([encoding[,errors]]) -> object
 |      '''編碼,將字元串編碼'''
 |      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.
 |  
 |  endswith(...)
 |      S.endswith(suffix[, start[, end]]) -> bool
 |      '''判斷字元串在某範圍內(範圍用索引指定,不指定預設是整個字元串)是否以指定的字元串(suffix)結尾,返回布爾值'''
 |      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.
 |  
 |  expandtabs(...)
 |      S.expandtabs([tabsize]) -> string
 |      '''將字元串里的製表符(一般用tab建輸入,也可以手動使用特殊字元 \t )轉換成空格,預設一個製表符轉換成8個空格,也可以指定個數(tabsize),並返回一個轉換後的副本'''
 |      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.
 |  
 |  find(...)
 |      S.find(sub [,start [,end]]) -> int
 |      '''在原字元串一定範圍內,尋找給定的字元串,找到了返回第一個被找到的字元的索引值,沒找到就返回-1'''
 |      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.
 |  
 |  format(...)
 |      S.format(*args, **kwargs) -> string
 |      '''字元串格式化（比%s更為高級，需要的話自行去瞭解），(*args, **kwargs)是處理函數傳參的一種方式，以後繼續講'''
 |      Return a formatted version of S, using substitutions from args and kwargs.
 |      The substitutions are identified by braces ('{' and '}').
 |  
 |  index(...)
 |      S.index(sub [,start [,end]]) -> int
 |      '''和S.find()作用一樣，只不過沒找到時會報錯'''
 |      Like S.find() but raise ValueError when the substring is not found.
 |  
 |  isalnum(...)
 |      S.isalnum() -> bool
 |      '''判斷字元串內是否由字母和數字組成，返回布爾值'''
 |      Return True if all characters in S are alphanumeric
 |      and there is at least one character in S, False otherwise.
 |  
 |  isalpha(...)
 |      S.isalpha() -> bool
 |      '''判斷字元串是否全是由字母組成，返回布爾值'''
 |      Return True if all characters in S are alphabetic
 |      and there is at least one character in S, False otherwise.
 |  
 |  isdigit(...)
 |      S.isdigit() -> bool
 |      '''判斷字元串是否全是由數字組成，返回布爾值'''
 |      Return True if all characters in S are digits
 |      and there is at least one character in S, False otherwise.
 |  
 |  islower(...)
 |      S.islower() -> bool
 |      '''判斷字元串里的所有字母是否都是小寫，當然，前提是字元串裡面最少有一個字母，返回布爾值'''
 |      Return True if all cased characters in S are lowercase and there is
 |      at least one cased character in S, False otherwise.
 |  
 |  isspace(...)
 |      S.isspace() -> bool
 |      '''判斷字元串是否都是由空白字元組成（空格），當然，前提是字元串裡面最少有一個空格，返回布爾值'''
 |      Return True if all characters in S are whitespace
 |      and there is at least one character in S, False otherwise.
 |  
 |  istitle(...)
 |      S.istitle() -> bool
 |      '''判斷字元串是否是標題，而標題的標準就是所有單詞的首字母都是大寫，其他的都是小寫，返回布爾值'''
 |      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.
 |  
 |  isupper(...)
 |      S.isupper() -> bool
 |      '''判斷字元串里的所有字母是否都是大寫，和小寫對應'''
 |      Return True if all cased characters in S are uppercase and there is
 |      at least one cased character in S, False otherwise.
 |  
 |  join(...)
 |      S.join(iterable) -> string
 |      '''字元串的拼接，詳情看我前面的博文'''
 |      Return a string which is the concatenation of the strings in the
 |      iterable.  The separator between elements is S.
 |  
 |  ljust(...)
 |      S.ljust(width[, fillchar]) -> string
 |      '''左對齊，關於對齊和填充可以看我上篇博文'''
 |      Return S left-justified in a string of length width. Padding is
 |      done using the specified fill character (default is a space).
 |  
 |  lower(...)
 |      S.lower() -> string
 |      '''返回一個全是小寫的字元串副本'''
 |      Return a copy of the string S converted to lowercase.
 |  
 |  lstrip(...)
 |      S.lstrip([chars]) -> string or unicode
 |      '''和strip類似，不過只去除左邊的空格，可以指定字元'''
 |      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
 |  
 |  partition(...)
 |      S.partition(sep) -> (head, sep, tail)
 |      '''和 split 的分隔類似，但返回的是元祖，不過 split 不過保留給定字元，translate 則會保留，並放在中間，沒找到則前後為空'''
 |      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.
 |  
 |  replace(...)
 |      S.replace(old, new[, count]) -> string
 |      '''替換，用新的字元串（new），替換原字元串里有的老字元串（old），用 count 指定替換的次數，不指定則全部替換'''
 |      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.
 |  
 |  rfind(...)
 |      S.rfind(sub [,start [,end]]) -> int
 |      '''和S.find()作用類似，不過尋找方向是從右向左'''
 |      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.
 |  
 |  rindex(...)
 |      S.rindex(sub [,start [,end]]) -> int
 |      '''和S.index()作用類似，不過尋找方向是從右向左'''
 |      Like S.rfind() but raise ValueError when the substring is not found.
 |  
 |  rjust(...)
 |      S.rjust(width[, fillchar]) -> string
 |      '''右對齊'''
 |      Return S right-justified in a string of length width. Padding is
 |      done using the specified fill character (default is a space)
 |  
 |  rpartition(...)
 |      S.rpartition(sep) -> (head, sep, tail)
 |      '''partition 的右邊操作版本'''
 |      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.
 |  
 |  rsplit(...)
 |      S.rsplit([sep [,maxsplit]]) -> list of strings
 |      '''split 的右邊操作版，要設置了 maxsplit 才能體現，否則都是全部分隔'''
 |      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.
 |  
 |  rstrip(...)
 |      S.rstrip([chars]) -> string or unicode
 |      '''和strip類似，不過只去除右邊的空格，可以指定字元'''
 |      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
 |  
 |  split(...)
 |      S.split([sep [,maxsplit]]) -> list of strings
 |      '''按照給定的字元進行分割（從左邊開始，找到的第一個），返回一個分割由後剩下的字元串組成的列表（不保留sep），
 |　　　　　 maxsplit 指定最大分割次數，否則凡是出現指定的分隔符都會分隔'''
 |      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.
 |  
 |  splitlines(...)
 |      S.splitlines(keepends=False) -> list of strings
 |      '''根據換行符分割'''
 |      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.
 |  
 |  startswith(...)
 |      S.startswith(prefix[, start[, end]]) -> bool
 |      '''判斷是否已指定字元串開頭，與上面的結尾判斷相對應'''
 |      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.
 |  
 |  strip(...)
 |      S.strip([chars]) -> string or unicode
 |      '''與 center 的填充相反，這裡是移除兩邊的填充，同樣也可以指定移除填充的字元，預設是空格，和 center 類似'''
 |      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
 |  
 |  swapcase(...)
 |      S.swapcase() -> string
 |      '''返回一個翻轉原字元串字母大小寫後的副本'''
 |      Return a copy of the string S with uppercase characters
 |      converted to lowercase and vice versa.
 |  
 |  title(...)
 |      S.title() -> string
 |      '''將字元串轉換為標題格式'''
 |      Return a titlecased version of S, i.e. words start with uppercase
 |      characters, all remaining cased characters have lowercase.
 |  
 |  translate(...)
 |      S.translate(table [,deletechars]) -> string
 |      '''根據參數table給出的表(翻譯表，翻譯表是通過maketrans方法轉換而來)轉換字元串的字元, 要過濾掉的字元放到 del 參數中'''
 |      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.
 |  
 |  upper(...)
 |      S.upper() -> string
 |      '''將字元串的字母全部大寫'''
 |      Return a copy of the string S converted to uppercase.
 |  
 |  zfill(...)
 |      S.zfill(width) -> string
 |      '''返回一個給定長度的字元串（小於原字元串無效），原字元右對齊，前面用0填充'''
 |      Pad a numeric string S with zeros on the left, to fill a field
 |      of the specified width.  The string S is never truncated.
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __new__ = <built-in method __new__ of type object>
 |      T.__new__(S, ...) -> a new object with type S, a subtype of T

 　　首先，我們要註意一個問題，所以的方法都沒有改變原字元串本身，都是返回了一個新對象，具體原理我會在講到函數中說明，而一個新的對象沒有把它賦值給一個變數的話，其引用數就為0，在python進行垃圾回收的時候，就會將其從記憶體中清除。

　　 另外，如果你英文夠好的話，其實使用 help() 函數就能夠自行學習了，所以這裡對幫助函數是一些要點進行說明：

　　1. <==> 表示相對於，意思這前後的方法效果是一樣的

　　2. -> 表示函數的返回值，意思是這個方法處理以後，返回的值是什麼類型，可以是字元串 string ，也可以是數字 int 等等。關於返回值的詳細，會在講函數的時候分析。

　　3.函數進行傳值的時候，對傳入的值的類型是有要求的，不然會有很多報錯，但這裡並沒有明說一定要傳什麼類型的值，而已在英文說明中隱含，所以需要一定的英語閱讀能力，英文不好就用經驗來堆吧。

 　　首先，我先來說說對於字元串來說，各運算符的含義：

　　1.+

　　　　代表字元串拼接，不多講了

　　2.in

　　　　表示給定的字元串是否在原字元串裡面，返回布爾值

　　3.==

　　　　判斷兩個字元串是否一樣，值相等就行，返回布爾值

　　4.===

　　　　判斷是否是統一對象，不僅值要相同，在記憶體中的地址也有一樣，返回布爾值

　　5.!=

　　　　不等於，值和對象都不相等，返回布爾值

　　5.<,>,<=,>=

　　　　字元串的大小判斷非常奇特，它是用每個字元逐一比較，比較的是字元對應的ascll編碼，例如：

a = 'a'    #以十進位的ascll為例，其為97
b = 'b'    #以十進位的ascll為例，其為98
a < b

　　　　另外，其是每個字元逐一比較的，一旦某個字元比另一個大，則整個字元串都大於另一個，例如

　　　　a只有一個字元，但比較的時候，是用 a 的第一個字元 'z' 和 b的第一個字元 'a' 比較，因為'z' > 'a' 了，所以整個字元串都大。如果逐一比較時，兩個字元相等的話，就比較下一個字元，如果比較到最後都相等，則說明兩個字元串的值相等（==）。至於是否是同一對象就需要另外確定。

　　6.*

　　　　字元串的乘法將會返回一個多出重覆原字元串的副本。

　　　　只能和數字相乘，字元串間相乘是不可以的。

　　　　也沒有什麼“乘法分配率”的說法，這樣只是重覆元祖而已。

　　7.%

　　　　取模運算符就是字元串格式化時使用的符號。

　　關於剩下的內置方法，我會另起一篇進行總結分析。