open_read_prototype = CFUNCTYPE( POINTER( sox_format_t ) , c_char_p , \
								sox_signalinfo_t , sox_encodinginfo_t , c_char_p )
open_read_paramflags = \
		( 1 , 'path' , None ) , \
		( 1 , 'signal' , None ) , \
		( 1 , 'encoding' , None ) , \
		( 1 , 'filetype' , None )
open_read = open_read_prototype( ( "sox_open_read" , libsox ) , open_read_paramflags )
open_read.errcheck = not_null_pointer


/home/ryan/<ipython console> in <module>()

/home/ryan/src/soxwrap.py in __init__(self, infile, outfile)
    330         def __init__( self , infile , outfile ):
    331                 format_init()
--> 332                 self.in_format = open_read( path=infile )
    333                 self.out_format = open_write( outfile , signal=self.in_format[0].signal )
    334 

<class 'ctypes.ArgumentError'>: argument 2: <type 'exceptions.TypeError'>: expected sox_signalinfo_t instance instead of NoneType