Python 字符串操作及string模块使用
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python的字符串操作通过2部分的方法函数基本上就可以解决所有的字符串操作需求：
- python的字符串属性函数
- python的string模块
1.字符串属性方法操作:
1.>字符串格式输出对齐
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>>> str = "Python stRING" >>> print str.center(20) #生成20个字符长度，str排中间 Python stRING >>> print str.ljust(20) #生成20个字符长度，str左对齐Python stRING >>> print str.rjust(20) #生成20个字符长度，str右对齐 Python stRING |
2.>大小写转换
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>>> str = "Python stRING">>> str.upper() #转大写‘PYTHON STRING‘>>> str.lower() #转小写 ‘python string‘>>> str.capitalize() #字符串首为大写，其余小写‘Python string‘>>> str.swapcase() #大小写对换 ‘pYTHON STring‘>>> str.title() #以分隔符为标记，首字符为大写，其余为小写‘Python String‘ |
3.>字符串条件判断
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>>> str = ‘01234‘>>> str.isalnum() #是否全是字母和数字，并至少有一个字符True>>> str.isdigit() #是否全是数字，并至少有一个字符True >>> str = ‘string‘>>> str.isalnum() #是否全是字母和数字，并至少有一个字符True>>> str.isalpha() #是否全是字母，并至少有一个字符 True>>> str.islower() #是否全是小写，当全是小写和数字一起时候，也判断为TrueTrue>>> str = "01234abcd">>> str.islower() #是否全是小写，当全是小写和数字一起时候，也判断为TrueTrue>>> str.isalnum() #是否全是字母和数字，并至少有一个字符True>>> str = ‘ ‘>>> str.isspace() #是否全是空白字符，并至少有一个字符True>>> str = ‘ABC‘>>> str.isupper() #是否全是大写，当全是大写和数字一起时候，也判断为TrueTrue>>> str = ‘Aaa Bbb‘>>> str.istitle() #所有单词字首都是大写，标题 True>>> str = ‘string learn‘>>> str.startswith(‘str‘) #判断字符串以‘str‘开头True>>> str.endswith(‘arn‘) #判读字符串以‘arn‘结尾True |
4.>字符串搜索定位与替换
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>>> str=‘string lEARn‘>>> str.find(‘z‘) #查找字符串，没有则返回-1，有则返回查到到第一个匹配的索引-1>>> str.find(‘n‘) #返回查到到第一个匹配的索引4>>> str.rfind(‘n‘) #返回的索引是最后一次匹配的11>>> str.index(‘a‘) #如果没有匹配则报错 Traceback (most recent call last): File "<input>", line 1, in <module>ValueError: substring not found >>> str.index("n") #同find类似,返回第一次匹配的索引值4>>> str.rindex("n") #返回最后一次匹配的索引值11>>> str.count(‘a‘) #字符串中匹配的次数0>>> str.count(‘n‘) #同上2>>> str.replace(‘EAR‘,‘ear‘) #匹配替换‘string learn‘>>> str.replace(‘n‘,‘N‘)‘striNg lEARN‘>>> str.replace(‘n‘,‘N‘,1)‘striNg lEARn‘>>> str.strip(‘n‘) #删除字符串首尾匹配的字符，通常用于默认删除回车符 ‘string lEAR‘ >>> str.lstrip(‘n‘) #左匹配 ‘string lEARn‘ >>> str.rstrip(‘n‘) #右匹配 ‘string lEAR‘ >>> str = " tab">>> str.expandtabs() #把制表符转为空格‘ tab‘>>> str.expandtabs(2) #指定空格数‘ tab‘ |
5.>字符串编码与解码
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>>> str = "字符串学习">>> str‘\\xe5\\xad\\x97\\xe7\\xac\\xa6\\xe4\\xb8\\xb2\\xe5\\xad\\xa6\\xe4\\xb9\\xa0‘>>> str.decode(‘utf-8‘) #解码过程，将utf-8解码为unicodeu‘\\u5b57\\u7b26\\u4e32\\u5b66\\u4e60‘>>> str.decode("utf-8").encode(‘gbk‘) #编码过程，将unicode编码为gbk‘\\xd7\\xd6\\xb7\\xfb\\xb4\\xae\\xd1\\xa7\\xcf\\xb0‘>>> str.decode(‘utf-8‘).encode(‘utf-8‘) #将unicode编码为utf-8 ‘\\xe5\\xad\\x97\\xe7\\xac\\xa6\\xe4\\xb8\\xb2\\xe5\\xad\\xa6\\xe4\\xb9\\xa0‘ |
6.>字符串分割变换
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>> str = "Learn string">>> ‘-‘.join(str)‘L-e-a-r-n- -s-t-r-i-n-g‘>>> li = [‘Learn‘,‘string‘]>>> ‘-‘.join(li)‘Learn-string‘>>> str.split(‘n‘)[‘Lear‘, ‘ stri‘, ‘g‘]>>> str.split(‘n‘,1)[‘Lear‘, ‘ string‘]>>> str.rsplit(‘n‘)[‘Lear‘, ‘ stri‘, ‘g‘]>>> str.rsplit(‘n‘,1)[‘Learn stri‘, ‘g‘]>>> str.splitlines()[‘Learn string‘]>>> str.partition(‘n‘)(‘Lear‘, ‘n‘, ‘ string‘)>>> str.rpartition(‘n‘)(‘Learn stri‘, ‘n‘, ‘g‘) |
2.string模块源代码
1 """A collection of string operations (most are no longer used). 2 3 Warning: most of the code you see here isn‘t normally used nowadays. 4 Beginning with Python 1.6, many of these functions are implemented as 5 methods on the standard string object. They used to be implemented by 6 a built-in module called strop, but strop is now obsolete itself. 7 8 Public module variables: 9 10 whitespace -- a string containing all characters considered whitespace 11 lowercase -- a string containing all characters considered lowercase letters 12 uppercase -- a string containing all characters considered uppercase letters 13 letters -- a string containing all characters considered letters 14 digits -- a string containing all characters considered decimal digits 15 hexdigits -- a string containing all characters considered hexadecimal digits 16 octdigits -- a string containing all characters considered octal digits 17 punctuation -- a string containing all characters considered punctuation 18 printable -- a string containing all characters considered printable 19 20 """ 21 22 # Some strings for ctype-style character classification 23 whitespace = ‘ \\t\\n\\r\\v\\f‘ 24 lowercase = ‘abcdefghijklmnopqrstuvwxyz‘ 25 uppercase = ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ‘ 26 letters = lowercase + uppercase 27 ascii_lowercase = lowercase 28 ascii_uppercase = uppercase 29 ascii_letters = ascii_lowercase + ascii_uppercase 30 digits = ‘0123456789‘ 31 hexdigits = digits + ‘abcdef‘ + ‘ABCDEF‘ 32 octdigits = ‘01234567‘ 33 punctuation = """!"#$%&‘()*+,-./:;<=>[email protected][\\]^_`{|}~""" 34 printable = digits + letters + punctuation + whitespace 35 36 # Case conversion helpers 37 # Use str to convert Unicode literal in case of -U 38 l = map(chr, xrange(256)) 39 _idmap = str(‘‘).join(l) 40 del l 41 42 # Functions which aren‘t available as string methods. 43 44 # Capitalize the words in a string, e.g. " aBc dEf " -> "Abc Def". 45 def capwords(s, sep=None): 46 """capwords(s [,sep]) -> string 47 48 Split the argument into words using split, capitalize each 49 word using capitalize, and join the capitalized words using 50 join. If the optional second argument sep is absent or None, 51 runs of whitespace characters are replaced by a single space 52 and leading and trailing whitespace are removed, otherwise 53 sep is used to split and join the words. 54 55 """ 56 return (sep or ‘ ‘).join(x.capitalize() for x in s.split(sep)) 57 58 59 # Construct a translation string 60 _idmapL = None 61 def maketrans(fromstr, tostr): 62 """maketrans(frm, to) -> string 63 64 Return a translation table (a string of 256 bytes long) 65 suitable for use in string.translate. The strings frm and to 66 must be of the same length. 67 68 """ 69 if len(fromstr) != len(tostr): 70 raise ValueError, "maketrans arguments must have same length" 71 global _idmapL 72 if not _idmapL: 73 _idmapL = list(_idmap) 74 L = _idmapL[:] 75 fromstr = map(ord, fromstr) 76 for i in range(len(fromstr)): 77 L[fromstr[i]] = tostr[i] 78 return ‘‘.join(L) 79 80 81 82 #################################################################### 83 import re as _re 84 85 class _multimap: 86 """Helper class for combining multiple mappings. 87 88 Used by .{safe_,}substitute() to combine the mapping and keyword 89 arguments. 90 """ 91 def __init__(self, primary, secondary): 92 self._primary = primary 93 self._secondary = secondary 94 95 def __getitem__(self, key): 96 try: 97 return self._primary[key] 98 except KeyError: 99 return self._secondary[key] 100 101 102 class _TemplateMetaclass(type): 103 pattern = r""" 104 %(delim)s(?: 105 (?P<escaped>%(delim)s) | # Escape sequence of two delimiters 106 (?P<named>%(id)s) | # delimiter and a Python identifier 107 {(?P<braced>%(id)s)} | # delimiter and a braced identifier 108 (?P<invalid>) # Other ill-formed delimiter exprs 109 ) 110 """ 111 112 def __init__(cls, name, bases, dct): 113 super(_TemplateMetaclass, cls).__init__(name, bases, dct) 114 if ‘pattern‘ in dct: 115 pattern = cls.pattern 116 else: 117 pattern = _TemplateMetaclass.pattern % { 118 ‘delim‘ : _re.escape(cls.delimiter), 119 ‘id‘ : cls.idpattern, 120 } 121 cls.pattern = _re.compile(pattern, _re.IGNORECASE | _re.VERBOSE) 122 123 124 class Template: 125 """A string class for supporting $-substitutions.""" 126 __metaclass__ = _TemplateMetaclass 127 128 delimiter = ‘$‘ 129 idpattern = r‘[_a-z][_a-z0-9]*‘ 130 131 def __init__(self, template): 132 self.template = template 133 134 # Search for $$, $identifier, ${identifier}, and any bare $‘s 135 136 def _invalid(self, mo): 137 i = mo.start(‘invalid‘) 138 lines = self.template[:i].splitlines(True) 139 if not lines: 140 colno = 1 141 lineno = 1 142 else: 143 colno = i - len(‘‘.join(lines[:-1])) 144 lineno = len(lines) 145 raise ValueError(‘Invalid placeholder in string: line %d, col %d‘ % 146 (lineno, colno)) 147 148 def substitute(*args, **kws): 149 if not args: 150 raise TypeError("descriptor ‘substitute‘ of ‘Template‘ object " 151 "needs an argument") 152 self, args = args[0], args[1:] # allow the "self" keyword be passed 153 if len(args) > 1: 154 raise TypeError(‘Too many positional arguments‘) 155 if not args: 156 mapping = kws 157 elif kws: 158 mapping = _multimap(kws, args[0]) 159 else: 160 mapping = args[0] 161 # Helper function for .sub() 162 def convert(mo): 163 # Check the most common path first. 164 named = mo.group(‘named‘) or mo.group(‘braced‘) 165 if named is not None: 166 val = mapping[named] 167 # We use this idiom instead of str() because the latter will 168 # fail if val is a Unicode containing non-ASCII characters. 169 return ‘%s‘ % (val,) 170 if mo.group(‘escaped‘) is not None: 171 return self.delimiter 172 if mo.group(‘invalid‘) is not None: 173 self._invalid(mo) 174 raise ValueError(‘Unrecognized named group in pattern‘, 175 self.pattern) 176 return self.pattern.sub(convert, self.template) 177 178 def safe_substitute(*args, **kws): 179 if not args: 180 raise TypeError("descriptor ‘safe_substitute‘ of ‘Template‘ object " 181 "needs an argument") 182 self, args = args[0], args[1:] # allow the "self" keyword be passed 183 if len(args) > 1: 184 raise TypeError(‘Too many positional arguments‘) 185 if not args: 186 mapping = kws 187 elif kws: 188 mapping = _multimap(kws, args[0]) 189 else: 190 mapping = args[0] 191 # Helper function for .sub() 192 def convert(mo): 193 named = mo.group(‘named‘) or mo.group(‘braced‘) 194 if named is not None: 195 try: 196 # We use this idiom instead of str() because the latter 197 # will fail if val is a Unicode containing non-ASCII 198 return ‘%s‘ % (mapping[named],) 199 except KeyError: 200 return mo.group() 201 if mo.group(‘escaped‘) is not None: 202 return self.delimiter 203 if mo.group(‘invalid‘) is not None: 204 return mo.group() 205 raise ValueError(‘Unrecognized named group in pattern‘, 206 self.pattern) 207 return self.pattern.sub(convert, self.template) 208 209 210 211 #################################################################### 212 # NOTE: Everything below here is deprecated. Use string methods instead. 213 # This stuff will go away in Python 3.0. 214 215 # Backward compatible names for exceptions 216 index_error = ValueError 217 atoi_error = ValueError 218 atof_error = ValueError 219 atol_error = ValueError 220 221 # convert UPPER CASE letters to lower case 222 def lower(s): 223 """lower(s) -> string 224 225 Return a copy of the string s converted to lowercase. 226 227 """ 228 return s.lower() 229 230 # Convert lower case letters to UPPER CASE 231 def upper(s): 232 """upper(s) -> string 233 234 Return a copy of the string s converted to uppercase. 235 236 """ 237 return s.upper() 238 239 # Swap lower case letters and UPPER CASE 240 def swapcase(s): 241 """swapcase(s) -> string 242 243 Return a copy of the string s with upper case characters 244 converted to lowercase and vice versa. 245 246 """ 247 return s.swapcase() 248 249 # Strip leading and trailing tabs and spaces 250 def strip(s, chars=None): 251 """strip(s [,chars]) -> string 252 253 Return a copy of the string s with leading and trailing 254 whitespace removed. 255 If chars is given and not None, remove characters in chars instead. 256 If chars is unicode, S will be converted to unicode before stripping. 257 258 """ 259 return s.strip(chars) 260 261 # Strip leading tabs and spaces 262 def lstrip(s, chars=None): 263 """lstrip(s [,chars]) -> string 264 265 Return a copy of the string s with leading whitespace removed. 266 If chars is given and not None, remove characters in chars instead. 267 268 """ 269 return s.lstrip(chars) 270 271 # Strip trailing tabs and spaces 272 def rstrip(s, chars=None): 273 """rstrip(s [,chars]) -> string 274 275 Return a copy of the string s with trailing whitespace removed. 276 If chars is given and not None, remove characters in chars instead. 277 278 """ 279 return s.rstrip(chars) 280 281 282 # Split a string into a list of space/tab-separated words 283 def split(s, sep=None, maxsplit=-1): 284 """split(s [,sep [,maxsplit]]) -> list of strings 285 286 Return a list of the words in the string s, using sep as the 287 delimiter string. If maxsplit is given, splits at no more than 288 maxsplit places (resulting in at most maxsplit+1 words). If sep 289 is not specified or is None, any whitespace string is a separator. 290 291 (split and splitfields are synonymous) 292 293 """ 294 return s.split(sep, maxsplit) 295 splitfields = split 296 297 # Split a string into a list of space/tab-separated words 298 def rsplit(s, sep=None, maxsplit=-1): 299 """rsplit(s [,sep [,maxsplit]]) -> list of strings 300 301 Return a list of the words in the string s, using sep as the 302 delimiter string, starting at the end of the string and working 303 to the front. If maxsplit is given, at most maxsplit splits are 304 done. If sep is not specified or is None, any whitespace string 305 is a separator. 306 """ 307 return s.rsplit(sep, maxsplit) 308 309 # Join fields with optional separator 310 def join(words, sep = ‘ ‘): 311 """join(list [,sep]) -> string 312 313 Return a string composed of the words in list, with 314 intervening occurrences of sep. The default separator is a 315 single space. 316 317 (joinfields and join are synonymous) 318 319 """ 320 return sep.join(words) 321 joinfields = join 322 323 # Find substring, raise exception if not found 324 def index(s, *args): 325 """index(s, sub [,start [,end]]) -> int 326 327 Like find but raises ValueError when the substring is not found. 328 329 """ 330 return s.index(*args) 331 332 # Find last substring, raise exception if not found 333 def rindex(s, *args): 334 """rindex(s, sub [,start [,end]]) -> int 335 336 Like rfind but raises ValueError when the substring is not found. 337 338 """ 339 return s.rindex(*args) 340 341 # Count non-overlapping occurrences of substring 342 def count(s, *args): 343 """count(s, sub[, start[,end]]) -> int 344 345 Return the number of occurrences of substring sub in string 346 s[start:end]. Optional arguments start and end are 347 interpreted as in slice notation. 348 349 """ 350 return s.count(*args) 351 352 # Find substring, return -1 if not found 353 def find(s, *args): 354 """find(s, sub [,start [,end]]) -> in 355 356 Return the lowest index in s where substring sub is found, 357 such that sub is contained within s[start,end]. Optional 358 arguments start and end are interpreted as in slice notation. 359 360 Return -1 on failure. 361 362 """ 363 return s.find(*args) 364 365 # Find last substring, return -1 if not found 366 def rfind(s, *args): 367 """rfind(s, sub [,start [,end]]) -> int 368 369 Return the highest index in s where substring sub is found, 370 such that sub is contained within s[start,end]. Optional 371 arguments start and end are interpreted as in slice notation. 372 373 Return -1 on failure. 374 375 """ 376 return s.rfind(*args) 377 378 # for a bit of speed 379 _float = float 380 _int = int 381 _long = long 382 383 # Convert string to float 384 def atof(s): 385 """atof(s) -> float 386 387 Return the floating point number represented by the string s. 388 389 """ 390 return _float(s) 391 392 393 # Convert string to integer 394 def atoi(s , base=10): 395 """atoi(s [,base]) -> int 396 397 Return the integer represented by the string s in the given 398 base, which defaults to 10. The string s must consist of one 399 or more digits, possibly preceded by a sign. If base is 0, it 400 is chosen from the leading characters of s, 0 for octal, 0x or 401 0X for hexadecimal. If base is 16, a preceding 0x or 0X is 402 accepted. 403 404 """ 405 return _int(s, base) 406 407 408 # Convert string to long integer 409 def atol(s, base=10): 410 """atol(s [,base]) -> long 411 412 Return the long integer represented by the string s in the 413 given base, which defaults to 10. The string s must consist 414 of one or more digits, possibly preceded by a sign. If base 415 is 0, it is chosen from the leading characters of s, 0 for 416 octal, 0x or 0X for hexadecimal. If base is 16, a preceding 417 0x or 0X is accepted. A trailing L or l is not accepted, 418 unless base is 0. 419 420 """ 421 return _long(s, base) 422 423 424 # Left-justify a string 425 def ljust(s, width, *args): 426 """ljust(s, width[, fillchar]) -> string 427 428 Return a left-justified version of s, in a field of the 429 specified width, padded with spaces as needed. The string is 430 never truncated. If specified the fillchar is used instead of spaces. 431 432 """ 433 return s.ljust(width, *args) 434 435 # Right-justify a string 436 def rjust(s, width, *args): 437 """rjust(s, width[, fillchar]) -> string 438 439 Return a right-justified version of s, in a field of the 440 specified width, padded with spaces as needed. The string is 441 never truncated. If specified the fillchar is used instead of spaces. 442 443 """ 444 return s.rjust(width, *args) 445 446 # Center a string 447 def center(s, width, *args): 448 """center(s, width[, fillchar]) -> string 449 450 Return a center version of s, in a field of the specified 451 width. padded with spaces as needed. The string is never 452 truncated. If specified the fillchar is used instead of spaces. 453 454 """ 455 return s.center(width, *args) 456 457 # Zero-fill a number, e.g., (12, 3) --> ‘012‘ and (-3, 3) --> ‘-03‘ 458 # Decadent feature: the argument may be a string or a number 459 # (Use of this is deprecated; it should be a string as with ljust c.s.) 460 def zfill(x, width): 461 """zfill(x, width) -> string 462 463 Pad a numeric string x with zeros on the left, to fill a field 464 of the specified width. The string x is never truncated. 465 466 """ 467 if not isinstance(x, basestring): 468 x = repr(x) 469 return x.zfill(width) 470 471 # Expand tabs in a string. 472 # Doesn‘t take non-printing chars into account, but does understand \\n. 473 def expandtabs(s, tabsize=8): 474 """expandtabs(s [,tabsize]) -> string 475 476 Return a copy of the string s with all tab characters replaced 477 by the appropriate number of spaces, depending on the current 478 column, and the tabsize (default 8). 479 480 """ 481 return s.expandtabs(tabsize) 482 483 # Character translation through look-up table. 484 def translate(s, table, deletions=""): 485 """translate(s,table [,deletions]) -> string 486 487 Return a copy of the string s, where all characters occurring 488 in the optional argument deletions are removed, and the 489 remaining characters have been mapped through the given 490 translation table, which must be a string of length 256. The 491 deletions argument is not allowed for Unicode strings. 492 493 """ 494 if deletions or table is None: 495 return s.translate(table, deletions) 496 else: 497 # Add s[:0] so that if s is Unicode and table is an 8-bit string, 498 # table is converted to Unicode. This means that table *cannot* 499 # be a dictionary -- for that feature, use u.translate() directly. 500 return s.translate(table + s[:0]) 501 502 # Capitalize a string, e.g. "aBc dEf" -> "Abc def". 503 def capitalize(s): 504 """capitalize(s) -> string 505 506 Return a copy of the string s with only its first character 507 capitalized. 508 509 """ 510 return s.capitalize() 511 512 # Substring replacement (global) 513 def replace(s, old, new, maxreplace=-1): 514 """replace (str, old, new[, maxreplace]) -> string 515 516 Return a copy of string str with all occurrences of substring 517 old replaced by new. If the optional argument maxreplace is 518 given, only the first maxreplace occurrences are replaced. 519 520 """ 521 return s.replace(old, new, maxreplace) 522 523 524 # Try importing optional built-in module "strop" -- if it exists, 525 # it redefines some string operations that are 100-1000 times faster. 526 # It also defines values for whitespace, lowercase and uppercase 527 # that match <ctype.h>‘s definitions. 528 529 try: 530 from strop import maketrans, lowercase, uppercase, whitespace 531 letters = lowercase + uppercase 532 except ImportError: 533 pass # Use the original versions 534 535 ######################################################################## 536 # the Formatter class 537 # see PEP 3101 for details and purpose of this class 538 539 # The hard parts are reused from the C implementation. They‘re exposed as "_" 540 # prefixed methods of str and unicode. 541 542 # The overall parser is implemented in str._formatter_parser. 543 # The field name parser is implemented in str._formatter_field_name_split 544 545 class Formatter(object): 546 def format(*args, **kwargs): 547 if not args: 548 raise TypeError("descriptor ‘format‘ of ‘Formatter‘ object " 549 "needs an argument") 550 self, args = args[0], args[1:] # allow the "self" keyword be passed 551 try: 552 format_string, args = args[0], args[1:] # allow the "format_string" keyword be passed 553 except IndexError: 554 if ‘format_string‘ in kwargs: 555 format_string = kwargs.pop(‘format_string‘) 556 else: 557 raise TypeError("format() missing 1 required positional " 558 "argument: ‘format_string‘") 559 return self.vformat(format_string, args, kwargs) 560 561 def vformat(self, format_string, args, kwargs): 562 used_args = set() 563 result = self._vformat(format_string, args, kwargs, used_args, 2) 564 self.check_unused_args(used_args, args, kwargs) 565 return result 566 567 def _vformat(self, format_string, args, kwargs, used_args, recursion_depth): 568 if recursion_depth < 0: 569 raise ValueError(‘Max string recursion exceeded‘) 570 result = [] 571 for literal_text, field_name, format_spec, conversion in 572 self.parse(format_string): 573 574 # output the literal text 575 if literal_text: 576 result.append(literal_text) 577 578 # if there‘s a field, output it 579 if field_name is not None: 580 # this is some markup, find the object and do 581 # the formatting 582 583 # given the field_name, find the object it references 584 # and the argument it came from 585 obj, arg_used = self.get_field(field_name, args, kwargs) 586 used_args.add(arg_used) 587 588 # do any conversion on the resulting object 589 obj = self.convert_field(obj, conversion) 590 591 # expand the format spec, if needed 592 format_spec = self._vformat(format_spec, args, kwargs, 593 used_args, recursion_depth-1) 594 595 # format the object and append to the result 596 result.append(self.format_field(obj, format_spec)) 597 598 return ‘‘.join(result) 599 600 601 def get_value(self, key, args, kwargs): 602 if isinstance(key, (int, long)): 603 return args[key] 604 else: 605 return kwargs[key] 606 607 608 def check_unused_args(self, used_args, args, kwargs): 609 pass 610 611 612 def format_field(self, value, format_spec): 613 return format(value, format_spec) 614 615 616 def convert_field(self, value, conversion): 617 # do any conversion on the resulting object 618 if conversion is None: 619 return value 620 elif conversion == ‘s‘: 621 return str(value) 622 elif conversion == ‘r‘: 623 return repr(value) 624 raise ValueError("Unknown conversion specifier {0!s}".format(conversion)) 625 626 627 # returns an iterable that contains tuples of the form: 628 # (literal_text, field_name, format_spec, conversion) 629 # literal_text can be zero length 630 # field_name can be None, in which case there‘s no 631 # object to format and output 632 # if field_name is not None, it is looked up, formatted 633 # with format_spec and conversion and then used 634 def parse(self, format_string): 635 return format_string._formatter_parser() 636 637 638 # given a field_name, find the object it references. 639 # field_name: the field being looked up, e.g. "0.name" 640 # or "lookup[3]" 641 # used_args: a set of which args have been used 642 # args, kwargs: as passed in to vformat 643 def get_field(self, field_name, args, kwargs): 644 first, rest = field_name._formatter_field_name_split() 645 646 obj = self.get_value(first, args, kwargs) 647 648 # loop through the rest of the field_name, doing 649 # getattr or getitem as needed 650 for is_attr, i in rest: 651 if is_attr: 652 obj = getattr(obj, i) 653 else: 654 obj = obj[i] 655 656 return obj, first