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( 
 47          [tuple([s.strip() for s in param.split("=", 1)]) 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   
 84   
 85   
 87      """Find the best match for a mime-type amongst parsed media-ranges. 
 88   
 89      Find the best match for a given mime-type against a list of media_ranges 
 90      that have already been parsed by parse_media_range(). Returns a tuple of 
 91      the fitness value and the value of the 'q' quality parameter of the best 
 92      match, or (-1, 0) if no match was found. Just as for quality_parsed(), 
 93      'parsed_ranges' must be a list of parsed media ranges. 
 94      """ 
 95      best_fitness = -1 
 96      best_fit_q = 0 
 97      (target_type, target_subtype, target_params) = parse_media_range(mime_type) 
 98      for (type, subtype, params) in parsed_ranges: 
 99          type_match = type == target_type or type == "*" or target_type == "*" 
100          subtype_match = ( 
101              subtype == target_subtype or subtype == "*" or target_subtype == "*" 
102          ) 
103          if type_match and subtype_match: 
104              param_matches = reduce( 
105                  lambda x, y: x + y, 
106                  [ 
107                      1 
108                      for (key, value) in six.iteritems(target_params) 
109                      if key != "q" and key in params and value == params[key] 
110                  ], 
111                  0, 
112              ) 
113              fitness = (type == target_type) and 100 or 0 
114              fitness += (subtype == target_subtype) and 10 or 0 
115              fitness += param_matches 
116              if fitness > best_fitness: 
117                  best_fitness = fitness 
118                  best_fit_q = params["q"] 
119   
120      return best_fitness, float(best_fit_q) 
 121   
122   
124      """Find the best match for a mime-type amongst parsed media-ranges. 
125   
126      Find the best match for a given mime-type against a list of media_ranges 
127      that have already been parsed by parse_media_range(). Returns the 'q' 
128      quality parameter of the best match, 0 if no match was found. This function 
129      bahaves the same as quality() except that 'parsed_ranges' must be a list of 
130      parsed media ranges. 
131      """ 
132   
133      return fitness_and_quality_parsed(mime_type, parsed_ranges)[1] 
 134   
135   
137      """Return the quality ('q') of a mime-type against a list of media-ranges. 
138   
139      Returns the quality 'q' of a mime-type when compared against the 
140      media-ranges in ranges. For example: 
141   
142      >>> quality('text/html','text/*;q=0.3, text/html;q=0.7, 
143                    text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5') 
144      0.7 
145   
146      """ 
147      parsed_ranges = [parse_media_range(r) for r in ranges.split(",")] 
148   
149      return quality_parsed(mime_type, parsed_ranges) 
 150   
151   
153      """Return mime-type with the highest quality ('q') from list of candidates. 
154   
155      Takes a list of supported mime-types and finds the best match for all the 
156      media-ranges listed in header. The value of header must be a string that 
157      conforms to the format of the HTTP Accept: header. The value of 'supported' 
158      is a list of mime-types. The list of supported mime-types should be sorted 
159      in order of increasing desirability, in case of a situation where there is 
160      a tie. 
161   
162      >>> best_match(['application/xbel+xml', 'text/xml'], 
163                     'text/*;q=0.5,*/*; q=0.1') 
164      'text/xml' 
165      """ 
166      split_header = _filter_blank(header.split(",")) 
167      parsed_header = [parse_media_range(r) for r in split_header] 
168      weighted_matches = [] 
169      pos = 0 
170      for mime_type in supported: 
171          weighted_matches.append( 
172              (fitness_and_quality_parsed(mime_type, parsed_header), pos, mime_type) 
173          ) 
174          pos += 1 
175      weighted_matches.sort() 
176   
177      return weighted_matches[-1][0][1] and weighted_matches[-1][2] or "" 
 178   
179   
181      for s in i: 
182          if s.strip(): 
183              yield s 
 184