字符串的定义
字符串或串(String)是由数字、字母、下划线组成的一串字符。它是编程语言中表示文本的数据类型。
一、 查看123和'123'的区别：
1 >>> a=123 2 3 >>> stra="123" 4 5 打印查看：结果显示一样 6 >>> print a 7 123 8 9 >>> print stra 10 123 11 12 13 14 交互式查看：区分引号 15 >>> a 16 123 17 18 >>> stra 19 '123' 20 21 显示类型查看：一个是数字，一个是字符 22 >>> type(a) 23 <type 'int'> 24 25 >>> type(stra) 26 <type 'str'> 27 28 29 计算2个变量发现：类型不匹配，字符串不能用于运算。 30 >>> a+stra 31 Traceback (most recent call last): 32 File "<stdin>", line 1, in <module> 33 TypeError: unsupported operand type(s) for +: 'int' and 'str'
二、字符串的取值：
python字符串有2种取值顺序：
从左到右索引默认0开始的，最大范围是字符串长度少1
从右到左索引默认-1开始的，最大范围是字符串开头
列表中的值得分割，也可以用到变量[头下标:尾下标]，又称切片。
它可以截取相应的列表，从左到右索引默认0开始的，从右到左索引默认-1开始。
下标可以为空表示取到头或尾。
它可以截取相应的列表，从左到右索引默认0开始的，从右到左索引默认-1开始。
下标可以为空表示取到头或尾。
1 #!/usr/bin/python 2 s = 'ilovepython' 3 print(s[1:5]) 4 5 输出结果： 6 love。
三、字符串的换行：
注意：这么定义不能真实反映出数据的状态，如果不加
、缩进、空格那将会显得非常乱
1 >>> mail='tom: hello i am jack' 2 3 >>> mail 4 'tom: hello i am jack' 5 6 >>> print mail 7 tom: 8 hello 9 i am jack
四、定义字符串的方法：
使用三个引号作为字符串格式的定义
1 >>> mail="""tom: 2 3 ... i am jack 4 ... goodbye 5 ... """ 6 7 8 >>> print (mail) 9 tom: 10 i am jack 11 goodbye 12 查看变量保存的格式： 13 14 15 >>> mail 16 'tom: i am jack goodbye '
五、三个引号也可以作为注释
1 #!/usr/bin/python 2 """input""" 3 a=int(raw_input("please input num1:")) 4 b=int(raw_input("please input num2:")) 5 print(a+b) 6 print(a-b) 7 print(a*b) 8 print(a/b) 9 10 显示结果： 11 [root@master1 pydata]# python 2.py 12 please input num1:3 13 please input num2:2 14 5 15 1 16 6 17 1
六、加号（+）是字符串连接运算符星号（*）是重复操作
1 str = 'Hello World!' 2 3 print(str) # 输出完整字符串 4 print(str[0]) # 输出字符串中的第一个字符 5 print(str[2:5]) # 输出字符串中第三个至第五个之间的字符串 6 print(str[2:]) # 输出从第三个字符开始的字符串 7 print(str * 2) # 输出字符串两次 8 print(str + "TEST") # 输出连接的字符串
1 Hello World! 2 H 3 llo 4 llo World! 5 Hello World!Hello World! 6 Hello World!TEST
字符串常用功能：
移除空白 ：print(str.split(" "))
分割：print(str.strip())
长度： len(str)
索： 详情请看《数据类型--索引和切片》
切片：详情请看《数据类型--索引和切片》
分割：print(str.strip())
长度： len(str)
索： 详情请看《数据类型--索引和切片》
切片：详情请看《数据类型--索引和切片》
1 class str(basestring): 2 """ 3 str(object='') -> string 4 5 Return a nice string representation of the object. 6 If the argument is a string, the return value is the same object. 7 """ 8 def capitalize(self): 9 """ 首字母变大写 """ 10 """ 11 S.capitalize() -> string 12 13 Return a copy of the string S with only its first character 14 capitalized. 15 """ 16 return "" 17 18 def center(self, width, fillchar=None): 19 """ 内容居中，width：总长度；fillchar：空白处填充内容，默认无 """ 20 """ 21 S.center(width[, fillchar]) -> string 22 23 Return S centered in a string of length width. Padding is 24 done using the specified fill character (default is a space) 25 """ 26 return "" 27 28 def count(self, sub, start=None, end=None): 29 """ 子序列个数 """ 30 """ 31 S.count(sub[, start[, end]]) -> int 32 33 Return the number of non-overlapping occurrences of substring sub in 34 string S[start:end]. Optional arguments start and end are interpreted 35 as in slice notation. 36 """ 37 return 0 38 39 def decode(self, encoding=None, errors=None): 40 """ 解码 """ 41 """ 42 S.decode([encoding[,errors]]) -> object 43 44 Decodes S using the codec registered for encoding. encoding defaults 45 to the default encoding. errors may be given to set a different error 46 handling scheme. Default is 'strict' meaning that encoding errors raise 47 a UnicodeDecodeError. Other possible values are 'ignore' and 'replace' 48 as well as any other name registered with codecs.register_error that is 49 able to handle UnicodeDecodeErrors. 50 """ 51 return object() 52 53 def encode(self, encoding=None, errors=None): 54 """ 编码，针对unicode """ 55 """ 56 S.encode([encoding[,errors]]) -> object 57 58 Encodes S using the codec registered for encoding. encoding defaults 59 to the default encoding. errors may be given to set a different error 60 handling scheme. Default is 'strict' meaning that encoding errors raise 61 a UnicodeEncodeError. Other possible values are 'ignore', 'replace' and 62 'xmlcharrefreplace' as well as any other name registered with 63 codecs.register_error that is able to handle UnicodeEncodeErrors. 64 """ 65 return object() 66 67 def endswith(self, suffix, start=None, end=None): 68 """ 是否以 xxx 结束 """ 69 """ 70 S.endswith(suffix[, start[, end]]) -> bool 71 72 Return True if S ends with the specified suffix, False otherwise. 73 With optional start, test S beginning at that position. 74 With optional end, stop comparing S at that position. 75 suffix can also be a tuple of strings to try. 76 """ 77 return False 78 79 def expandtabs(self, tabsize=None): 80 """ 将tab转换成空格，默认一个tab转换成8个空格 """ 81 """ 82 S.expandtabs([tabsize]) -> string 83 84 Return a copy of S where all tab characters are expanded using spaces. 85 If tabsize is not given, a tab size of 8 characters is assumed. 86 """ 87 return "" 88 89 def find(self, sub, start=None, end=None): 90 """ 寻找子序列位置，如果没找到，返回 -1 """ 91 """ 92 S.find(sub [,start [,end]]) -> int 93 94 Return the lowest index in S where substring sub is found, 95 such that sub is contained within S[start:end]. Optional 96 arguments start and end are interpreted as in slice notation. 97 98 Return -1 on failure. 99 """ 100 return 0 101 102 def format(*args, **kwargs): # known special case of str.format 103 """ 字符串格式化，动态参数，将函数式编程时细说 """ 104 """ 105 S.format(*args, **kwargs) -> string 106 107 Return a formatted version of S, using substitutions from args and kwargs. 108 The substitutions are identified by braces ('{' and '}'). 109 """ 110 pass 111 112 def index(self, sub, start=None, end=None): 113 """ 子序列位置，如果没找到，报错 """ 114 S.index(sub [,start [,end]]) -> int 115 116 Like S.find() but raise ValueError when the substring is not found. 117 """ 118 return 0 119 120 def isalnum(self): 121 """ 是否是字母和数字 """ 122 """ 123 S.isalnum() -> bool 124 125 Return True if all characters in S are alphanumeric 126 and there is at least one character in S, False otherwise. 127 """ 128 return False 129 130 def isalpha(self): 131 """ 是否是字母 """ 132 """ 133 S.isalpha() -> bool 134 135 Return True if all characters in S are alphabetic 136 and there is at least one character in S, False otherwise. 137 """ 138 return False 139 140 def isdigit(self): 141 """ 是否是数字 """ 142 """ 143 S.isdigit() -> bool 144 145 Return True if all characters in S are digits 146 and there is at least one character in S, False otherwise. 147 """ 148 return False 149 150 def islower(self): 151 """ 是否小写 """ 152 """ 153 S.islower() -> bool 154 155 Return True if all cased characters in S are lowercase and there is 156 at least one cased character in S, False otherwise. 157 """ 158 return False 159 160 def isspace(self): 161 """ 162 S.isspace() -> bool 163 164 Return True if all characters in S are whitespace 165 and there is at least one character in S, False otherwise. 166 """ 167 return False 168 169 def istitle(self): 170 """ 171 S.istitle() -> bool 172 173 Return True if S is a titlecased string and there is at least one 174 character in S, i.e. uppercase characters may only follow uncased 175 characters and lowercase characters only cased ones. Return False 176 otherwise. 177 """ 178 return False 179 180 def isupper(self): 181 """ 182 S.isupper() -> bool 183 184 Return True if all cased characters in S are uppercase and there is 185 at least one cased character in S, False otherwise. 186 """ 187 return False 188 189 def join(self, iterable): 190 """ 连接 """ 191 """ 192 S.join(iterable) -> string 193 194 Return a string which is the concatenation of the strings in the 195 iterable. The separator between elements is S. 196 """ 197 return "" 198 199 def ljust(self, width, fillchar=None): 200 """ 内容左对齐，右侧填充 """ 201 """ 202 S.ljust(width[, fillchar]) -> string 203 204 Return S left-justified in a string of length width. Padding is 205 done using the specified fill character (default is a space). 206 """ 207 return "" 208 209 def lower(self): 210 """ 变小写 """ 211 """ 212 S.lower() -> string 213 214 Return a copy of the string S converted to lowercase. 215 """ 216 return "" 217 218 def lstrip(self, chars=None): 219 """ 移除左侧空白 """ 220 """ 221 S.lstrip([chars]) -> string or unicode 222 223 Return a copy of the string S with leading whitespace removed. 224 If chars is given and not None, remove characters in chars instead. 225 If chars is unicode, S will be converted to unicode before stripping 226 """ 227 return "" 228 229 def partition(self, sep): 230 """ 分割，前，中，后三部分 """ 231 """ 232 S.partition(sep) -> (head, sep, tail) 233 234 Search for the separator sep in S, and return the part before it, 235 the separator itself, and the part after it. If the separator is not 236 found, return S and two empty strings. 237 """ 238 pass 239 240 def replace(self, old, new, count=None): 241 """ 替换 """ 242 """ 243 S.replace(old, new[, count]) -> string 244 245 Return a copy of string S with all occurrences of substring 246 old replaced by new. If the optional argument count is 247 given, only the first count occurrences are replaced. 248 """ 249 return "" 250 251 def rfind(self, sub, start=None, end=None): 252 """ 253 S.rfind(sub [,start [,end]]) -> int 254 255 Return the highest index in S where substring sub is found, 256 such that sub is contained within S[start:end]. Optional 257 arguments start and end are interpreted as in slice notation. 258 259 Return -1 on failure. 260 """ 261 return 0 262 263 def rindex(self, sub, start=None, end=None): 264 """ 265 S.rindex(sub [,start [,end]]) -> int 266 267 Like S.rfind() but raise ValueError when the substring is not found. 268 """ 269 return 0 270 271 def rjust(self, width, fillchar=None): 272 """ 273 S.rjust(width[, fillchar]) -> string 274 275 Return S right-justified in a string of length width. Padding is 276 done using the specified fill character (default is a space) 277 """ 278 return "" 279 280 def rpartition(self, sep): 281 """ 282 S.rpartition(sep) -> (head, sep, tail) 283 284 Search for the separator sep in S, starting at the end of S, and return 285 the part before it, the separator itself, and the part after it. If the 286 separator is not found, return two empty strings and S. 287 """ 288 pass 289 290 def rsplit(self, sep=None, maxsplit=None): 291 """ 292 S.rsplit([sep [,maxsplit]]) -> list of strings 293 294 Return a list of the words in the string S, using sep as the 295 delimiter string, starting at the end of the string and working 296 to the front. If maxsplit is given, at most maxsplit splits are 297 done. If sep is not specified or is None, any whitespace string 298 is a separator. 299 """ 300 return [] 301 302 def rstrip(self, chars=None): 303 """ 304 S.rstrip([chars]) -> string or unicode 305 306 Return a copy of the string S with trailing whitespace removed. 307 If chars is given and not None, remove characters in chars instead. 308 If chars is unicode, S will be converted to unicode before stripping 309 """ 310 return "" 311 312 def split(self, sep=None, maxsplit=None): 313 """ 分割， maxsplit最多分割几次 """ 314 """ 315 S.split([sep [,maxsplit]]) -> list of strings 316 317 Return a list of the words in the string S, using sep as the 318 delimiter string. If maxsplit is given, at most maxsplit 319 splits are done. If sep is not specified or is None, any 320 whitespace string is a separator and empty strings are removed 321 from the result. 322 """ 323 return [] 324 325 def splitlines(self, keepends=False): 326 """ 根据换行分割 """ 327 """ 328 S.splitlines(keepends=False) -> list of strings 329 330 Return a list of the lines in S, breaking at line boundaries. 331 Line breaks are not included in the resulting list unless keepends 332 is given and true. 333 """ 334 return [] 335 336 def startswith(self, prefix, start=None, end=None): 337 """ 是否起始 """ 338 """ 339 S.startswith(prefix[, start[, end]]) -> bool 340 341 Return True if S starts with the specified prefix, False otherwise. 342 With optional start, test S beginning at that position. 343 With optional end, stop comparing S at that position. 344 prefix can also be a tuple of strings to try. 345 """ 346 return False 347 348 def strip(self, chars=None): 349 """ 移除两段空白 """ 350 """ 351 S.strip([chars]) -> string or unicode 352 353 Return a copy of the string S with leading and trailing 354 whitespace removed. 355 If chars is given and not None, remove characters in chars instead. 356 If chars is unicode, S will be converted to unicode before stripping 357 """ 358 return "" 359 360 def swapcase(self): 361 """ 大写变小写，小写变大写 """ 362 """ 363 S.swapcase() -> string 364 365 Return a copy of the string S with uppercase characters 366 converted to lowercase and vice versa. 367 """ 368 return "" 369 370 def title(self): 371 """ 372 S.title() -> string 373 374 Return a titlecased version of S, i.e. words start with uppercase 375 characters, all remaining cased characters have lowercase. 376 """ 377 return "" 378 379 def translate(self, table, deletechars=None): 380 """ 381 转换，需要先做一个对应表，最后一个表示删除字符集合 382 intab = "aeiou" 383 outtab = "12345" 384 trantab = maketrans(intab, outtab) 385 str = "this is string example....wow!!!" 386 print str.translate(trantab, 'xm') 387 """ 388 389 """ 390 S.translate(table [,deletechars]) -> string 391 392 Return a copy of the string S, where all characters occurring 393 in the optional argument deletechars are removed, and the 394 remaining characters have been mapped through the given 395 translation table, which must be a string of length 256 or None. 396 If the table argument is None, no translation is applied and 397 the operation simply removes the characters in deletechars. 398 """ 399 return "" 400 401 def upper(self): 402 """ 403 S.upper() -> string 404 405 Return a copy of the string S converted to uppercase. 406 """ 407 return "" 408 409 def zfill(self, width): 410 """方法返回指定长度的字符串，原字符串右对齐，前面填充0。""" 411 """ 412 S.zfill(width) -> string 413 414 Pad a numeric string S with zeros on the left, to fill a field 415 of the specified width. The string S is never truncated. 416 """ 417 return "" 418 419 def _formatter_field_name_split(self, *args, **kwargs): # real signature unknown 420 pass 421 422 def _formatter_parser(self, *args, **kwargs): # real signature unknown 423 pass 424 425 def __add__(self, y): 426 """ x.__add__(y) <==> x+y """ 427 pass 428 429 def __contains__(self, y): 430 """ x.__contains__(y) <==> y in x """ 431 pass 432 433 def __eq__(self, y): 434 """ x.__eq__(y) <==> x==y """ 435 pass 436 437 def __format__(self, format_spec): 438 """ 439 S.__format__(format_spec) -> string 440 441 Return a formatted version of S as described by format_spec. 442 """ 443 return "" 444 445 def __getattribute__(self, name): 446 """ x.__getattribute__('name') <==> x.name """ 447 pass 448 449 def __getitem__(self, y): 450 """ x.__getitem__(y) <==> x[y] """ 451 pass 452 453 def __getnewargs__(self, *args, **kwargs): # real signature unknown 454 pass 455 456 def __getslice__(self, i, j): 457 """ 458 x.__getslice__(i, j) <==> x[i:j] 459 460 Use of negative indices is not supported. 461 """ 462 pass 463 464 def __ge__(self, y): 465 """ x.__ge__(y) <==> x>=y """ 466 pass 467 468 def __gt__(self, y): 469 """ x.__gt__(y) <==> x>y """ 470 pass 471 472 def __hash__(self): 473 """ x.__hash__() <==> hash(x) """ 474 pass 475 476 def __init__(self, string=''): # known special case of str.__init__ 477 """ 478 str(object='') -> string 479 480 Return a nice string representation of the object. 481 If the argument is a string, the return value is the same object. 482 # (copied from class doc) 483 """ 484 pass 485 486 def __len__(self): 487 """ x.__len__() <==> len(x) """ 488 pass 489 490 def __le__(self, y): 491 """ x.__le__(y) <==> x<=y """ 492 pass 493 494 def __lt__(self, y): 495 """ x.__lt__(y) <==> x<y """ 496 pass 497 498 def __mod__(self, y): 499 """ x.__mod__(y) <==> x%y """ 500 pass 501 502 def __mul__(self, n): 503 """ x.__mul__(n) <==> x*n """ 504 pass 505 506 @staticmethod # known case of __new__ 507 def __new__(S, *more): 508 """ T.__new__(S, ...) -> a new object with type S, a subtype of T """ 509 pass 510 511 def __ne__(self, y): 512 """ x.__ne__(y) <==> x!=y """ 513 pass 514 515 def __repr__(self): 516 """ x.__repr__() <==> repr(x) """ 517 pass 518 519 def __rmod__(self, y): 520 """ x.__rmod__(y) <==> y%x """ 521 pass 522 523 def __rmul__(self, n): 524 """ x.__rmul__(n) <==> n*x """ 525 pass 526 527 def __sizeof__(self): 528 """ S.__sizeof__() -> size of S in memory, in bytes """ 529 pass 530 531 def __str__(self): 532 """ x.__str__() <==> str(x) """ 533 pass
字符串的练习
1 name = "my name is alex" 2 3 #首字母大写： 4 print(name.capitalize()) 5 6 #判断变量是包含几个a 7 print(name.count("a")) 8 9 #左右填充，用“-”号代替 10 print(name.center(50,"-")) 11 12 #右填充，用“-”号代替 13 print("右填充",name.ljust(50,'-')) 14 15 #左填充，用“-”号代替 16 print("左填充",name.rjust(50,'-')) 17 18 19 #把字符串转成二进制： 20 a = name.encode() 21 print(a,type(a)) 22 23 #判断一个字符串以什么为结尾 24 print(name.endswith("ex")) 25 26 27 #在 的位置打印多少个空格 28 text1 = "my name is dongye" 29 print(text1.expandtabs()) 30 31 #找到并取出字符的索引 32 print(name.find("e")) 33 print(name[name.find("name"):]) #可以用作切片 34 35 #格式化变量里面的字符串： 36 text2 = "my name is {name} and i am {year} old" 37 print(text2.format(name='alix',year=23)) 38 39 40 #同format用法一样： 41 text3 = "my name is {name} and i am {year} old" 42 print(text3.format_map({'name':'alex','year':12})) 43 44 45 #是否包含阿拉伯数字： 46 print(name.isalnum()) 47 print('a1232'.isalnum()) 48 49 #判断是否为整数 50 print(name.isdigit()) 51 print("A1是否为整形：",'A1'.isdigit()) 52 print("22是否为整形：",'22'.isdigit()) 53 54 55 #判断是不是一个合法的标识符 56 print('a A1'.isidentifier()) 57 58 #判断是否为 59 print("判断a是否为小写：",'a'.islower()) 60 61 62 #判断是否为大写： 63 print("判断是否为大写:",'DONGYE'.isupper()) 64 65 66 #把大写转为小写： 67 print("大写转小写："'Alex'.lower()) 68 69 #把小写转为大写： 70 print("小写转大写："'Alex'.upper()) 71 72 73 #判断是否为空格： 74 print("判读是否为空格",' '.isnumeric()) 75 76 77 #判断每个字符首字母是否为大写： 78 print("每个字符串首字母是否为大写：",'My Name Is '.istitle()) 79 80 81 #字符串间加特殊符号、字符、表达式 82 print('+'.join(['a','b','c','d'])) 83 84 85 #去掉左面的回车和空格 86 print("去掉左面的回车和空格：",' Alex'.lstrip()) 87 88 #去掉右面面的回车和空格 89 print("去掉右面的回车和空格：",'Alex '.rstrip()) 90 print("---") 91 92 93 #去掉左右两边的回车和空格： 94 print("去掉右面的回车和空格：",' Alex '.strip()) 95 96 97 #可以当做随机密码： 98 p = str.maketrans("abcdef",'123456') 99 print("alexli".translate(p)) 100 101 102 #替换所有和单个字符： 103 #replace('源字符','替换字符',第几个) 104 print("所有小写l替换成大写L：",'alex li'.replace('l','L')) 105 print("所有小写l替换成大写L：",'aieix li ding lei'.replace('i','L',3)) 106 107 #查找最后一个指定值的下标： 108 print("从左往右数找到最后一个'l'下标",'alex lil'.rfind('l')) 109 110 111 #去掉or按照指定字符分割成列表： 112 print("字符串按照指定字符分割成列表：",'alex li'.split( )) 113 print("字符串按照指定字符分割成列表：",'a+2+3+4'.split('+')) #常用 114 print("字符串按照指定字符分割成列表：",'a+2+3+4'.split(' ')) 115 print("字符串按照指定字符分割成列表：",'a+2 +3+4'.splitlines()) #识别不同系统的换行。 116 117 #判断以什么为开头： 118 print('AlexLi'.startswith('A')) 119 120 #大写变小写，小写变大写： 121 print('AlexLi'.swapcase()) 122 123 124 #每个字符首字母改成大写： 125 print('al ex li'.title())