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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__ = "0.1.3"
__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("=", 1)])\
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. The list of supported mime-types should be sorted
in order of increasing desirability, in case of a situation
where there is a tie
>>> 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 _filter_blank(header.split(","))]
weighted_matches = []
pos = 0
for mime_type in supported:
weighted_matches.append((fitness_and_quality_parsed(mime_type,
parsed_header), pos, mime_type))
pos += 1
weighted_matches.sort()
return weighted_matches[-1][0][1] and weighted_matches[-1][2] or ''
def _filter_blank(i):
for s in i:
if s.strip():
yield s
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