[GRASS-user] v.extract where clause with puthon script

[Roy]

Dear all,

i'm trying to extract some vectors using attribute names using python 
script: (grass 6.4.4)

i have a column with "des" values : river, canal
and i have to extract only the features of type 'canal'
then of type 'river' and so on...

#######################################

import grass.script as grass

env = grass.gisenv()

grass.run_command('v.extract', input='idro', output='canal_idro', 
where='des = canal', overwrite='True')

#################################################################################

maybe i'm missing the correct sintiax of the "where" clause  because i 
only get
a buffer overflow as result,

thanks for any help,

Roy.