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mimeparse.py
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mimeparse.py
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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 explaination.
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
Contents:
- parse_mime_type(): Parses a mime-type into it's 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__ = "0.1.1"
__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:] ])
(type, subtype) = parts[0].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 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. """
best_fitness = -1
best_match = ""
best_fit_q = 0
(target_type, target_subtype, target_params) =\
parse_media_range(mime_type)
for (type, subtype, params) in parsed_ranges:
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)
if (type == target_type or type == '*' or target_type == '*') and \
(subtype == target_subtype or subtype == '*' or target_subtype == '*'):
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 float(best_fit_q)
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 = [(quality_parsed(mime_type, parsed_header), mime_type)\
for mime_type in supported]
weighted_matches.sort()
return weighted_matches[-1][0] and weighted_matches[-1][1] or ''
if __name__ == "__main__":
import unittest
class TestMimeParsing(unittest.TestCase):
def test_parse_media_range(self):
self.assert_(('application', 'xml', {'q': '1'}) == parse_media_range('application/xml;q=1'))
self.assertEqual(('application', 'xml', {'q': '1'}), parse_media_range('application/xml'))
self.assertEqual(('application', 'xml', {'q': '1'}), parse_media_range('application/xml;q='))
self.assertEqual(('application', 'xml', {'q': '1'}), parse_media_range('application/xml ; q='))
self.assertEqual(('application', 'xml', {'q': '1', 'b': 'other'}), parse_media_range('application/xml ; q=1;b=other'))
self.assertEqual(('application', 'xml', {'q': '1', 'b': 'other'}), parse_media_range('application/xml ; q=2;b=other'))
def test_rfc_2616_example(self):
accept = "text/*;q=0.3, text/html;q=0.7, text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5"
self.assertEqual(1, quality("text/html;level=1", accept))
self.assertEqual(0.7, quality("text/html", accept))
self.assertEqual(0.3, quality("text/plain", accept))
self.assertEqual(0.5, quality("image/jpeg", accept))
self.assertEqual(0.4, quality("text/html;level=2", accept))
self.assertEqual(0.7, quality("text/html;level=3", accept))
def test_best_match(self):
mime_types_supported = ['application/xbel+xml', 'application/xml']
# direct match
self.assertEqual(best_match(mime_types_supported, 'application/xbel+xml'), 'application/xbel+xml')
# direct match with a q parameter
self.assertEqual(best_match(mime_types_supported, 'application/xbel+xml; q=1'), 'application/xbel+xml')
# direct match of our second choice with a q parameter
self.assertEqual(best_match(mime_types_supported, 'application/xml; q=1'), 'application/xml')
# match using a subtype wildcard
self.assertEqual(best_match(mime_types_supported, 'application/*; q=1'), 'application/xml')
# match using a type wildcard
self.assertEqual(best_match(mime_types_supported, '*/*'), 'application/xml')
mime_types_supported = ['application/xbel+xml', 'text/xml']
# match using a type versus a lower weighted subtype
self.assertEqual(best_match(mime_types_supported, 'text/*;q=0.5,*/*; q=0.1'), 'text/xml')
# fail to match anything
self.assertEqual(best_match(mime_types_supported, 'text/html,application/atom+xml; q=0.9'), '')
def test_support_wildcards(self):
mime_types_supported = ['image/*', 'application/xml']
# match using a type wildcard
self.assertEqual(best_match(mime_types_supported, 'image/png'), 'image/*')
# match using a wildcard for both requested and supported
self.assertEqual(best_match(mime_types_supported, 'image/*'), 'image/*')
unittest.main()