Python 字符串操作及string模块使用详解编程语言

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

>>> 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

>>> 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

>>> 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True  
True 
 
>>> 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True 
True 
 
>>> 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True 
True 
 
>>> 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

>>> 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

>>> 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unicode  
u'/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

>> 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 = """!"#$%&'()*+,-./:;<=>?@[/]^_`{|}~""" 
 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

 

  

  

  

  

  

 

 

 

  

原创文章,作者:ItWorker,如若转载,请注明出处:https://blog.ytso.com/11660.html

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