<s> import cpa . util <EOL> class Preprocessor ( object ) : <EOL> pass <EOL> class NullPreprocessor ( Preprocessor ) : <EOL> def __init__ ( self , variables ) : <EOL> self . variables = variables <EOL> def __call__ ( self , data ) : <EOL> return data <EOL> class VariableSelector ( Preprocessor ) : <EOL> def __init__ ( self , mask , variables ) : <EOL> assert len ( mask ) == len ( variables ) <EOL> self . mask = mask <EOL> self . variables = [ v for v , m in zip ( variables , mask ) if m ] <EOL> def __call__ ( self , data ) : <EOL> return data [ : , self . mask ] </s>
