1   
  2   
  3   
  4   
  5  """MIME-Type Parser 
  6   
  7  This module provides basic functions for handling mime-types. It can handle 
  8  matching mime-types against a list of media-ranges. See section 14.1 of the 
  9  HTTP specification [RFC 2616] for a complete explanation. 
 10   
 11     http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1 
 12   
 13  Contents: 
 14   - parse_mime_type():   Parses a mime-type into its component parts. 
 15   - parse_media_range(): Media-ranges are mime-types with wild-cards and a 'q' 
 16                            quality parameter. 
 17   - quality():           Determines the quality ('q') of a mime-type when 
 18                            compared against a list of media-ranges. 
 19   - quality_parsed():    Just like quality() except the second parameter must be 
 20                            pre-parsed. 
 21   - best_match():        Choose the mime-type with the highest quality ('q') 
 22                            from a list of candidates. 
 23  """ 
 24  from __future__ import absolute_import 
 25  from functools import reduce 
 26  import six 
 27   
 28  __version__ = '0.1.3' 
 29  __author__ = 'Joe Gregorio' 
 30  __email__ = 'joe@bitworking.org' 
 31  __license__ = 'MIT License' 
 32  __credits__ = '' 
 33   
 34   
 36      """Parses a mime-type into its component parts. 
 37   
 38      Carves up a mime-type and returns a tuple of the (type, subtype, params) 
 39      where 'params' is a dictionary of all the parameters for the media range. 
 40      For example, the media range 'application/xhtml;q=0.5' would get parsed 
 41      into: 
 42   
 43         ('application', 'xhtml', {'q', '0.5'}) 
 44         """ 
 45      parts = mime_type.split(';') 
 46      params = dict([tuple([s.strip() for s in param.split('=', 1)])\ 
 47              for param in parts[1:] 
 48                    ]) 
 49      full_type = parts[0].strip() 
 50       
 51       
 52      if full_type == '*': 
 53          full_type = '*/*' 
 54      (type, subtype) = full_type.split('/') 
 55   
 56      return (type.strip(), subtype.strip(), params) 
  57   
 58   
 80   
 81   
 83      """Find the best match for a mime-type amongst parsed media-ranges. 
 84   
 85      Find the best match for a given mime-type against a list of media_ranges 
 86      that have already been parsed by parse_media_range(). Returns a tuple of 
 87      the fitness value and the value of the 'q' quality parameter of the best 
 88      match, or (-1, 0) if no match was found. Just as for quality_parsed(), 
 89      'parsed_ranges' must be a list of parsed media ranges. 
 90      """ 
 91      best_fitness = -1 
 92      best_fit_q = 0 
 93      (target_type, target_subtype, target_params) =\ 
 94              parse_media_range(mime_type) 
 95      for (type, subtype, params) in parsed_ranges: 
 96          type_match = (type == target_type or\ 
 97                        type == '*' or\ 
 98                        target_type == '*') 
 99          subtype_match = (subtype == target_subtype or\ 
100                           subtype == '*' or\ 
101                           target_subtype == '*') 
102          if type_match and subtype_match: 
103              param_matches = reduce(lambda x, y: x + y, [1 for (key, value) in \ 
104                      six.iteritems(target_params) if key != 'q' and \ 
105                      key in params and value == params[key]], 0) 
106              fitness = (type == target_type) and 100 or 0 
107              fitness += (subtype == target_subtype) and 10 or 0 
108              fitness += param_matches 
109              if fitness > best_fitness: 
110                  best_fitness = fitness 
111                  best_fit_q = params['q'] 
112   
113      return best_fitness, float(best_fit_q) 
 114   
115   
117      """Find the best match for a mime-type amongst parsed media-ranges. 
118   
119      Find the best match for a given mime-type against a list of media_ranges 
120      that have already been parsed by parse_media_range(). Returns the 'q' 
121      quality parameter of the best match, 0 if no match was found. This function 
122      bahaves the same as quality() except that 'parsed_ranges' must be a list of 
123      parsed media ranges. 
124      """ 
125   
126      return fitness_and_quality_parsed(mime_type, parsed_ranges)[1] 
 127   
128   
130      """Return the quality ('q') of a mime-type against a list of media-ranges. 
131   
132      Returns the quality 'q' of a mime-type when compared against the 
133      media-ranges in ranges. For example: 
134   
135      >>> quality('text/html','text/*;q=0.3, text/html;q=0.7, 
136                    text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5') 
137      0.7 
138   
139      """ 
140      parsed_ranges = [parse_media_range(r) for r in ranges.split(',')] 
141   
142      return quality_parsed(mime_type, parsed_ranges) 
 143   
144   
146      """Return mime-type with the highest quality ('q') from list of candidates. 
147   
148      Takes a list of supported mime-types and finds the best match for all the 
149      media-ranges listed in header. The value of header must be a string that 
150      conforms to the format of the HTTP Accept: header. The value of 'supported' 
151      is a list of mime-types. The list of supported mime-types should be sorted 
152      in order of increasing desirability, in case of a situation where there is 
153      a tie. 
154   
155      >>> best_match(['application/xbel+xml', 'text/xml'], 
156                     'text/*;q=0.5,*/*; q=0.1') 
157      'text/xml' 
158      """ 
159      split_header = _filter_blank(header.split(',')) 
160      parsed_header = [parse_media_range(r) for r in split_header] 
161      weighted_matches = [] 
162      pos = 0 
163      for mime_type in supported: 
164          weighted_matches.append((fitness_and_quality_parsed(mime_type, 
165                                   parsed_header), pos, mime_type)) 
166          pos += 1 
167      weighted_matches.sort() 
168   
169      return weighted_matches[-1][0][1] and weighted_matches[-1][2] or '' 
 170   
171   
173      for s in i: 
174          if s.strip(): 
175              yield s 
 176