'Return a list of features. Each feature is a tuple made of the specific
item feature and the opinion strength about that feature.
:param fileids: a list or regexp specifying the ids of the files whose
features have to be returned.
:return: all features for the item(s) in the given file(s).
:rtype: list(tuple)'

def features(self, fileids=None):

    if (fileids is None):
        fileids = self._fileids
    elif isinstance(fileids, string_types):
        fileids = [fileids]
    return concat([self.CorpusView(fileid, self._read_features, encoding=enc) for (fileid, enc) in self.abspaths(fileids, True)])
