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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
+
+Based on mimeparse 0.1.2 by Joe Gregorio:
+
+    http://code.google.com/p/mimeparse/
+
+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.
+    - desired_matches():   Filter against a list of desired mime-types in the order the server prefers.
+
+"""
+
+
+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'})
+       """
+    type = mime_type.split(';')
+    type, plist = type[0], type[1:]
+    try:
+        type, subtype = type.split('/', 1)
+    except ValueError:
+        type, subtype = type.strip() or '*', '*'
+    else:
+        type = type.strip() or '*'
+        subtype = subtype.strip() or '*'
+    params = {}
+    for param in plist:
+        param = param.split('=', 1)
+        if len(param) == 2:
+            key, value = param[0].strip(), param[1].strip()
+            if key and value:
+                params[key] = value
+    return type, subtype, 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)
+    try:
+        if not 0 <= float(params['q']) <= 1:
+            raise ValueError
+    except (KeyError, ValueError):
+        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, best_fit_q = -1, 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 == '*'):
+            fitness = 0
+            if type == target_type:
+                fitness += 100
+            if subtype == target_subtype:
+                fitness += 10
+            for key in target_params:
+                if key != 'q' and key in params:
+                    if params[key] == target_params[key]:
+                        fitness += 1
+            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 behaves 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 = map(parse_media_range, 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. In case of
+    ambiguity, whatever comes first in the list will be chosen.
+    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'
+    """
+    if not supported:
+        return ''
+    parsed_header = list(map(parse_media_range, header.split(',')))
+    best_type = max([
+            (fitness_and_quality_parsed(mime_type, parsed_header), -n)
+            for n, mime_type in enumerate(supported)])
+    return best_type[0][1] and supported[-best_type[1]] or ''
+
+def desired_matches(desired, header):
+    """Takes a list of desired mime-types in the order the server prefers to
+    send them regardless of the browsers preference.
+
+    Browsers (such as Firefox) technically want XML over HTML depending on how
+    one reads the specification. This function is provided for a server to
+    declare a set of desired mime-types it supports, and returns a subset of
+    the desired list in the same order should each one be Accepted by the
+    browser.
+
+    >>> desired_matches(['text/html', 'application/xml'], \
+    ...     'text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png')
+    ['text/html', 'application/xml']
+    >>> desired_matches(['text/html', 'application/xml'], 'application/xml,application/json')
+    ['application/xml']
+    """
+    parsed_ranges = list(map(parse_media_range, header.split(',')))
+    return [mimetype for mimetype in desired
+        if quality_parsed(mimetype, parsed_ranges)]
+