6.python字符串-内置方法列举
所谓内置方法，就是凡是字符串都能用的方法，这个方法在创建字符串的类中，下面是总结：
首先，我们要学习一个获取帮助的内置函数 help(对象) ，对象可以是一个我们创建出来的，也可以是创建对象的那个类，类也是一个对象，被称为类对象。
当我们进入解释器的交互模式中输入以下代码时：
help(str)
其中，str就是创建字符串的类，然后我们就会得到一长串的结果：
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 #字符串拼接，看+号就知道 | | __contains__(...) | x.__contains__(y) <==> y in x #判断x里字符是否在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 #获取属性 | | __getitem__(...) | x.__getitem__(y) <==> x[y] #索引取值，详情参考python中的序列 | | __getnewargs__(...) | | __getslice__(...) | x.__getslice__(i, j) <==> x[i:j] #切片，也是序列的一种方法 | | 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 #用字节表示在内存中的大小 | | __str__(...) | x.__str__() <==> str(x) | | capitalize(...) | S.capitalize() -> string | '''返回首字母大写字符串副本,对中文无效''' | Return a copy of the string S with only its first character | capitalized. | | center(...) | S.center(width[, fillchar]) -> string | '''返回指定宽度（width）的字符串副本，原字符串居中对齐，可指定用什么来填充多余部分（fillchar）默认为空格，关于对齐和填充可以看上篇博文的解释''' | 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 | '''计数器，返回给定字符串在原字符串出现的次数，也可指定范围''' | 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 | '''解码，将字符串解码成某种字符集''' | 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 | '''编码,将字符串编码''' | 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 | '''判断字符串在某范围内(范围用索引指定,不指定默认是整个字符串)是否以指定的字符串(suffix)结尾,返回布尔值''' | 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 | '''将字符串里的制表符(一般用tab建输入,也可以手动使用特殊字符 \t )转换成空格,默认一个制表符转换成8个空格,也可以指定个数(tabsize),并返回一个转换后的副本''' | 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 | '''在原字符串一定范围内,寻找给定的字符串,找到了返回第一个被找到的字符的索引值,没找到就返回-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 | '''字符串格式化（比%s更为高级，需要的话自行去了解），(*args, **kwargs)是处理函数传参的一种方式，以后继续讲''' | 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()作用一样，只不过没找到时会报错''' | Like S.find() but raise ValueError when the substring is not found. | | isalnum(...) | S.isalnum() -> bool | '''判断字符串内是否由字母和数字组成，返回布尔值''' | Return True if all characters in S are alphanumeric | and there is at least one character in S, False otherwise. | | isalpha(...) | S.isalpha() -> bool | '''判断字符串是否全是由字母组成，返回布尔值''' | Return True if all characters in S are alphabetic | and there is at least one character in S, False otherwise. | | isdigit(...) | S.isdigit() -> bool | '''判断字符串是否全是由数字组成，返回布尔值''' | Return True if all characters in S are digits | and there is at least one character in S, False otherwise. | | islower(...) | S.islower() -> bool | '''判断字符串里的所有字母是否都是小写，当然，前提是字符串里面最少有一个字母，返回布尔值''' | 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 | '''判断字符串是否都是由空白字符组成（空格），当然，前提是字符串里面最少有一个空格，返回布尔值''' | Return True if all characters in S are whitespace | and there is at least one character in S, False otherwise. | | istitle(...) | S.istitle() -> bool | '''判断字符串是否是标题，而标题的标准就是所有单词的首字母都是大写，其他的都是小写，返回布尔值''' | 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 | '''判断字符串里的所有字母是否都是大写，和小写对应''' | 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 | '''字符串的拼接，详情看我前面的博文''' | 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 | '''左对齐，关于对齐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 | '''返回一个全是小写的字符串副本''' | Return a copy of the string S converted to lowercase. | | lstrip(...) | S.lstrip([chars]) -> string or unicode | '''和strip类似，不过只去除左边的空格，可以指定字符''' | 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 的分隔类似，但返回的是元祖，不过 split 不过保留给定字符，translate 则会保留，并放在中间，没找到则前后为空''' | 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 | '''替换，用新的字符串（new），替换原字符串里有的老字符串（old），用 count 指定替换的次数，不指定则全部替换''' | 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()作用类似，不过寻找方向是从右向左''' | 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()作用类似，不过寻找方向是从右向左''' | Like S.rfind() but raise ValueError when the substring is not found. | | rjust(...) | S.rjust(width[, fillchar]) -> string | '''右对齐''' | 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 的右边操作版本''' | 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 的右边操作版，要设置了 maxsplit 才能体现，否则都是全部分隔''' | 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类似，不过只去除右边的空格，可以指定字符''' | 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 | '''按照给定的字符进行分割（从左边开始，找到的第一个），返回一个分割由后剩下的字符串组成的列表（不保留sep）， | maxsplit 指定最大分割次数，否则凡是出现指定的分隔符都会分隔''' | 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 | '''根据换行符分割''' | 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 | '''判断是否已指定字符串开头，与上面的结尾判断相对应''' | 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 | '''与 center 的填充相反，这里是移除两边的填充，同样也可以指定移除填充的字符，默认是空格，和 center 类似''' | 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 | '''返回一个翻转原字符串字母大小写后的副本''' | Return a copy of the string S with uppercase characters | converted to lowercase and vice versa. | | title(...) | S.title() -> string | '''将字符串转换为标题格式''' | 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 | '''根据参数table给出的表(翻译表，翻译表是通过maketrans方法转换而来)转换字符串的字符, 要过滤掉的字符放到 del 参数中''' | 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 | '''将字符串的字母全部大写''' | Return a copy of the string S converted to uppercase. | | zfill(...) | S.zfill(width) -> string | '''返回一个给定长度的字符串（小于原字符串无效），原字符右对齐，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，我们要注意一个问题，所以的方法都没有改变原字符串本身，都是返回了一个新对象，具体原理我会在讲到函数中说明，而一个新的对象没有把它赋值给一个变量的话，其引用数就为0，在python进行垃圾回收的时候，就会将其从内存中清除。
另外，如果你英文够好的话，其实使用 help() 函数就能够自行学习了，所以这里对帮助函数是一些要点进行说明：
1. <==> 表示相对于，意思这前后的方法效果是一样的
2. -> 表示函数的返回值，意思是这个方法处理以后，返回的值是什么类型，可以是字符串 string ，也可以是数字 int 等等。关于返回值的详细，会在讲函数的时候分析。
3.函数进行传值的时候，对传入的值的类型是有要求的，不然会有很多报错，但这里并没有明说一定要传什么类型的值，而已在英文说明中隐含，所以需要一定的英语阅读能力，英文不好就用经验来堆吧。
首先，我先来说说对于字符串来说，各运算符的含义：
1.+
代表字符串拼接，不多讲了
2.in
表示给定的字符串是否在原字符串里面，返回布尔值
3.==
判断两个字符串是否一样，值相等就行，返回布尔值
4.is
判断是否是统一对象，不仅值要相同，在内存中的地址也有一样，返回布尔值
5.!=
不等于，值和对象都不相等，返回布尔值
5.<,>,<=,>=
字符串的大小判断非常奇特，它是用每个字符逐一比较，比较的是字符对应的ascll编码，例如：
a = 'a' #以十进制的ascll为例，其为97 b = 'b' #以十进制的ascll为例，其为98 a < b
另外，其是每个字符逐一比较的，一旦某个字符比另一个大，则整个字符串都大于另一个，例如
a只有一个字符，但比较的时候，是用 a 的第一个字符 'z' 和 b的第一个字符 'a' 比较，因为'z' > 'a' 了，所以整个字符串都大。如果逐一比较时，两个字符相等的话，就比较下一个字符，如果比较到最后都相等，则说明两个字符串的值相等（==）。至于是否是同一对象就需要另外确定。
6.*
字符串的乘法将会返回一个多出重复原字符串的副本。
只能和数字相乘，字符串间相乘是不可以的。
也没有什么“乘法分配率”的说法，这样只是重复元祖而已。
7.%
取模运算符就是字符串格式化时使用的符号。
关于剩下的内置方法，我会另起一篇进行总结分析。
