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"""MIME-Type Parser |
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This module provides basic functions for handling mime-types. It can handle |
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matching mime-types against a list of media-ranges. See section 14.1 of the |
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HTTP specification [RFC 2616] for a complete explanation. |
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http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1 |
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Contents: |
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- parse_mime_type(): Parses a mime-type into its component parts. |
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- parse_media_range(): Media-ranges are mime-types with wild-cards and a 'q' |
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quality parameter. |
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- quality(): Determines the quality ('q') of a mime-type when |
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compared against a list of media-ranges. |
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- quality_parsed(): Just like quality() except the second parameter must be |
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pre-parsed. |
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- best_match(): Choose the mime-type with the highest quality ('q') |
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from a list of candidates. |
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""" |
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from __future__ import absolute_import |
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from functools import reduce |
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__version__ = "0.1.3" |
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__author__ = "Joe Gregorio" |
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__email__ = "joe@bitworking.org" |
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__license__ = "MIT License" |
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__credits__ = "" |
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def parse_mime_type(mime_type): |
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"""Parses a mime-type into its component parts. |
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Carves up a mime-type and returns a tuple of the (type, subtype, params) |
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where 'params' is a dictionary of all the parameters for the media range. |
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For example, the media range 'application/xhtml;q=0.5' would get parsed |
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into: |
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('application', 'xhtml', {'q', '0.5'}) |
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""" |
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parts = mime_type.split(";") |
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params = dict( |
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[tuple([s.strip() for s in param.split("=", 1)]) for param in parts[1:]] |
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) |
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full_type = parts[0].strip() |
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if full_type == "*": |
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full_type = "*/*" |
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(type, subtype) = full_type.split("/") |
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return (type.strip(), subtype.strip(), params) |
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def parse_media_range(range): |
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"""Parse a media-range into its component parts. |
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Carves up a media range and returns a tuple of the (type, subtype, |
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params) where 'params' is a dictionary of all the parameters for the media |
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range. For example, the media range 'application/*;q=0.5' would get parsed |
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into: |
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('application', '*', {'q', '0.5'}) |
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In addition this function also guarantees that there is a value for 'q' |
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in the params dictionary, filling it in with a proper default if |
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necessary. |
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""" |
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(type, subtype, params) = parse_mime_type(range) |
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if ( |
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"q" not in params |
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or not params["q"] |
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or not float(params["q"]) |
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or float(params["q"]) > 1 |
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or float(params["q"]) < 0 |
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): |
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params["q"] = "1" |
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return (type, subtype, params) |
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def fitness_and_quality_parsed(mime_type, parsed_ranges): |
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"""Find the best match for a mime-type amongst parsed media-ranges. |
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Find the best match for a given mime-type against a list of media_ranges |
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that have already been parsed by parse_media_range(). Returns a tuple of |
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the fitness value and the value of the 'q' quality parameter of the best |
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match, or (-1, 0) if no match was found. Just as for quality_parsed(), |
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'parsed_ranges' must be a list of parsed media ranges. |
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""" |
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best_fitness = -1 |
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best_fit_q = 0 |
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(target_type, target_subtype, target_params) = parse_media_range(mime_type) |
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for (type, subtype, params) in parsed_ranges: |
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type_match = type == target_type or type == "*" or target_type == "*" |
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subtype_match = ( |
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subtype == target_subtype or subtype == "*" or target_subtype == "*" |
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) |
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if type_match and subtype_match: |
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param_matches = reduce( |
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lambda x, y: x + y, |
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[ |
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1 |
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for (key, value) in target_params.items() |
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if key != "q" and key in params and value == params[key] |
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], |
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0, |
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) |
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fitness = (type == target_type) and 100 or 0 |
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fitness += (subtype == target_subtype) and 10 or 0 |
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fitness += param_matches |
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if fitness > best_fitness: |
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best_fitness = fitness |
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best_fit_q = params["q"] |
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return best_fitness, float(best_fit_q) |
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def quality_parsed(mime_type, parsed_ranges): |
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"""Find the best match for a mime-type amongst parsed media-ranges. |
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Find the best match for a given mime-type against a list of media_ranges |
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that have already been parsed by parse_media_range(). Returns the 'q' |
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quality parameter of the best match, 0 if no match was found. This function |
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bahaves the same as quality() except that 'parsed_ranges' must be a list of |
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parsed media ranges. |
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""" |
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return fitness_and_quality_parsed(mime_type, parsed_ranges)[1] |
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def quality(mime_type, ranges): |
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"""Return the quality ('q') of a mime-type against a list of media-ranges. |
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Returns the quality 'q' of a mime-type when compared against the |
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media-ranges in ranges. For example: |
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>>> quality('text/html','text/*;q=0.3, text/html;q=0.7, |
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text/html;level=1, text/html;level=2;q=0.4, */*;q=0.5') |
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0.7 |
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""" |
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parsed_ranges = [parse_media_range(r) for r in ranges.split(",")] |
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return quality_parsed(mime_type, parsed_ranges) |
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def best_match(supported, header): |
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"""Return mime-type with the highest quality ('q') from list of candidates. |
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Takes a list of supported mime-types and finds the best match for all the |
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media-ranges listed in header. The value of header must be a string that |
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conforms to the format of the HTTP Accept: header. The value of 'supported' |
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is a list of mime-types. The list of supported mime-types should be sorted |
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in order of increasing desirability, in case of a situation where there is |
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a tie. |
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>>> best_match(['application/xbel+xml', 'text/xml'], |
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'text/*;q=0.5,*/*; q=0.1') |
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'text/xml' |
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""" |
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split_header = _filter_blank(header.split(",")) |
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parsed_header = [parse_media_range(r) for r in split_header] |
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weighted_matches = [] |
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pos = 0 |
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for mime_type in supported: |
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weighted_matches.append( |
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(fitness_and_quality_parsed(mime_type, parsed_header), pos, mime_type) |
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) |
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pos += 1 |
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weighted_matches.sort() |
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return weighted_matches[-1][0][1] and weighted_matches[-1][2] or "" |
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def _filter_blank(i): |
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for s in i: |
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if s.strip(): |
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yield s |
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