[web2py] how to restrict a field to be alphabet only

[Saurabh S]

hi i am developing a system in which i require a validation on name
field...validation shoould be : the field should not accept
numbers ...it should only accept alphabets...i know this is possible
using IS_MATCH in web2py...i tried using
db.organisations.name.requires=[IS_MATCH('^[a-z]',
error_message='This
is not a valid name')]
but it is not working
 please help me out.....