# Source code for surprise.reader

    '''This module contains the Reader class.'''

    from __future__ import (absolute_import, division, print_function,
                            unicode_literals)

    from .builtin_datasets import BUILTIN_DATASETS

    class Reader():
        """The Reader class is used to parse a file containing ratings.

        Such a file is assumed to specify only one rating per line, and each line
        needs to respect the following structure: ::

            user ; item ; rating ; [timestamp]

        where the order of the fields and the separator (here ';') may be
        arbitrarily defined (see below).  brackets indicate that the timestamp
        field is optional.

        For each built-in dataset, Surprise also provides predefined readers which
        are useful if you want to use a custom dataset that has the same format as
        a built-in one (see the ``name`` parameter).

        Args:
            name(:obj:`string`, optional): If specified, a Reader for one of the
                built-in datasets is returned and any other parameter is ignored.
                Accepted values are 'ml-100k', 'ml-1m', and 'jester'. Default
                is ``None``.
            line_format(:obj:`string`): The fields names, in the order at which
                they are encountered on a line. Please note that ``line_format`` is
                always space-separated (use the ``sep`` parameter). Default is
                ``'user item rating'``.
            sep(char): the separator between fields. Example : ``';'``.
            rating_scale(:obj:`tuple`, optional): The rating scale used for every
                rating.  Default is ``(1, 5)``.
            skip_lines(:obj:`int`, optional): Number of lines to skip at the
                beginning of the file. Default is ``0``.

        """

        def __init__(self, name=None, line_format='user item rating', sep=None,
                     rating_scale=(1, 5), skip_lines=0):

            if name:
                try:
                    self.__init__(**BUILTIN_DATASETS[name].reader_params)
                except KeyError:
                    raise ValueError('unknown reader ' + name +
                                     '. Accepted values are ' +
                                     ', '.join(BUILTIN_DATASETS.keys()) + '.')
            else:
                self.sep = sep
                self.skip_lines = skip_lines
                self.rating_scale = rating_scale

                lower_bound, higher_bound = rating_scale

                splitted_format = line_format.split()

                entities = ['user', 'item', 'rating']
                if 'timestamp' in splitted_format:
                    self.with_timestamp = True
                    entities.append('timestamp')
                else:
                    self.with_timestamp = False

                # check that all fields are correct
                if any(field not in entities for field in splitted_format):
                    raise ValueError('line_format parameter is incorrect.')

                self.indexes = [splitted_format.index(entity) for entity in
                                entities]

        def parse_line(self, line):
            '''Parse a line.

            Ratings are translated so that they are all strictly positive.

            Args:
                line(str): The line to parse

            Returns:
                tuple: User id, item id, rating and timestamp. The timestamp is set
                to ``None`` if it does no exist.
                '''

            line = line.split(self.sep)
            try:
                if self.with_timestamp:
                    uid, iid, r, timestamp = (line[i].strip()
                                              for i in self.indexes)
                else:
                    uid, iid, r = (line[i].strip()
                                   for i in self.indexes)
                    timestamp = None

            except IndexError:
                raise ValueError('Impossible to parse line. Check the line_format'
                                 ' and sep parameters.')

            return uid, iid, float(r), timestamp