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+"""MIME-Type Parser
+
+This module provides basic functions for handling mime-types. It can handle
+matching mime-types against a list of media-ranges. See section 14.1 of
+the HTTP specification [RFC 2616] for a complete explanation.
+
+ http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
+
+Contents:
+ - parse_mime_type(): Parses a mime-type into its component parts.
+ - parse_media_range(): Media-ranges are mime-types with wild-cards and a 'q' quality parameter.
+ - quality(): Determines the quality ('q') of a mime-type when compared against a list of media-ranges.
+ - quality_parsed(): Just like quality() except the second parameter must be pre-parsed.
+ - best_match(): Choose the mime-type with the highest quality ('q') from a list of candidates.
+"""
+
+__version__ = "0.1.2"
+__author__ = 'Joe Gregorio'
+__email__ = "joe@bitworking.org"
+__credits__ = ""
+
+def parse_mime_type(mime_type):
+ """Carves up a mime-type and returns a tuple of the
+ (type, subtype, params) where 'params' is a dictionary
+ of all the parameters for the media range.
+ For example, the media range 'application/xhtml;q=0.5' would
+ get parsed into:
+
+ ('application', 'xhtml', {'q', '0.5'})
+ """
+ parts = mime_type.split(";")
+ params = dict([tuple([s.strip() for s in param.split("=")])\
+ for param in parts[1:] ])
+ full_type = parts[0].strip()
+ # Java URLConnection class sends an Accept header that includes a single "*"
+ # Turn it into a legal wildcard.
+ if full_type == '*': full_type = '*/*'
+ (type, subtype) = full_type.split("/")
+ return (type.strip(), subtype.strip(), params)
+
+def parse_media_range(range):
+ """Carves up a media range and returns a tuple of the
+ (type, subtype, params) where 'params' is a dictionary
+ of all the parameters for the media range.
+ For example, the media range 'application/*;q=0.5' would
+ get parsed into:
+
+ ('application', '*', {'q', '0.5'})
+
+ In addition this function also guarantees that there
+ is a value for 'q' in the params dictionary, filling it
+ in with a proper default if necessary.
+ """
+ (type, subtype, params) = parse_mime_type(range)
+ if not params.has_key('q') or not params['q'] or \
+ not float(params['q']) or float(params['q']) > 1\
+ or float(params['q']) < 0:
+ params['q'] = '1'
+ return (type, subtype, params)
+
+def fitness_and_quality_parsed(mime_type, parsed_ranges):
+ """Find the best match for a given mime-type against
+ a list of media_ranges that have already been
+ parsed by parse_media_range(). Returns a tuple of
+ the fitness value and the value of the 'q' quality
+ parameter of the best match, or (-1, 0) if no match
+ was found. Just as for quality_parsed(), 'parsed_ranges'
+ must be a list of parsed media ranges. """
+ best_fitness = -1
+ best_fit_q = 0
+ (target_type, target_subtype, target_params) =\
+ parse_media_range(mime_type)
+ for (type, subtype, params) in parsed_ranges:
+ if (type == target_type or type == '*' or target_type == '*') and \
+ (subtype == target_subtype or subtype == '*' or target_subtype == '*'):
+ param_matches = reduce(lambda x, y: x+y, [1 for (key, value) in \
+ target_params.iteritems() if key != 'q' and \
+ params.has_key(key) and value == params[key]], 0)
+ fitness = (type == target_type) and 100 or 0
+ fitness += (subtype == target_subtype) and 10 or 0
+ fitness += param_matches
+ if fitness > best_fitness:
+ best_fitness = fitness
+ best_fit_q = params['q']
+
+ return best_fitness, float(best_fit_q)
+
+def quality_parsed(mime_type, parsed_ranges):
+ """Find the best match for a given mime-type against
+ a list of media_ranges that have already been
+ parsed by parse_media_range(). Returns the
+ 'q' quality parameter of the best match, 0 if no
+ match was found. This function bahaves the same as quality()
+ except that 'parsed_ranges' must be a list of
+ parsed media ranges. """
+ return fitness_and_quality_parsed(mime_type, parsed_ranges)[1]
+
+def quality(mime_type, ranges):
+ """Returns the quality 'q' of a mime-type when compared
+ against the media-ranges in ranges. For example:
+
+ >>> quality('text/html','text/*;q=0.3, text/html;q=0.7, text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5')
+ 0.7
+
+ """
+ parsed_ranges = [parse_media_range(r) for r in ranges.split(",")]
+ return quality_parsed(mime_type, parsed_ranges)
+
+def best_match(supported, header):
+ """Takes a list of supported mime-types and finds the best
+ match for all the media-ranges listed in header. The value of
+ header must be a string that conforms to the format of the
+ HTTP Accept: header. The value of 'supported' is a list of
+ mime-types.
+
+ >>> best_match(['application/xbel+xml', 'text/xml'], 'text/*;q=0.5,*/*; q=0.1')
+ 'text/xml'
+ """
+ parsed_header = [parse_media_range(r) for r in header.split(",")]
+ weighted_matches = [(fitness_and_quality_parsed(mime_type, parsed_header), mime_type)\
+ for mime_type in supported]
+ weighted_matches.sort()
+ return weighted_matches[-1][0][1] and weighted_matches[-1][1] or ''