'create a preprocessor object that will concatenate together the
given list of features'

def __init__(self, feature_list=DEFAULT_FEATURES):

    self.output_dim = 0
    self.feature_list = feature_list
    self.processors = ([None] * len(feature_list))
    for i in range(len(feature_list)):
        feat = feature_list[i].lower()
        if (feat in FEATURES):
            self.processors[i] = FEATURES[feat]['function']
            self.output_dim += FEATURES[feat]['size']
        else:
            raise ValueError(('uknown    feature:    %s' % feat))
