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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'
__license__ = 'MIT License'
__credits__ = ''
def parse_mime_type(mime_type):
"""Parses a mime-type into its component parts.
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):
"""Parse a media-range into its component parts.
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 'q' not in params 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 mime-type amongst parsed media-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:
type_match = (type == target_type or\
type == '*' or\
target_type == '*')
subtype_match = (subtype == target_subtype or\
subtype == '*' or\
target_subtype == '*')
if type_match and subtype_match:
param_matches = sum([1 for (key, value) in \
target_params.items() if key != 'q' and \
key in params 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 mime-type amongst parsed media-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):
"""Return the quality ('q') of a mime-type against a list of media-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):
"""Return mime-type with the highest quality ('q') from list of candidates.
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'
"""
split_header = _filter_blank(header.split(','))
parsed_header = [parse_media_range(r) for r in split_header]
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