python - formencode Schema add fields dynamically -

let's take, example, user schema site admin sets number of requested phone numbers:

class myschema(schema):     name = validators.string(not_empty=true)     phone_1 = validators.phonenumber(not_empty=true)     phone_2 = validators.phonenumber(not_empty=true)     phone_3 = validators.phonenumber(not_empty=true)     ... 

somehow thought do:

class myschema(schema):     name = validators.string(not_empty=true)     def __init__(self, *args, **kwargs):         requested_phone_numbers = session.query(...).scalar()         n in xrange(requested_phone_numbers):             key = 'phone_{0}'.format(n)             kwargs[key] = validators.phonenumber(not_empty=true)         schema.__init__(self, *args, **kwargs) 

since read in formencode docs:

validators use instance variables store customization information. can use either subclassing or normal instantiation set these.

and schema called in docs compound validator , subclass of fancyvalidator guessed it's correct.

but not work: added phone_n ignored , name required.

update:

also tried both overriding __new__ , __classinit__ before asking no success...

i had same problem, found solution here: http://markmail.org/message/m5ckyaml36eg2w3m

all thing use add_field method of schema in youre init method

class myschema(schema):     name = validators.string(not_empty=true)      def __init__(self, *args, **kwargs):         requested_phone_numbers = session.query(...).scalar()         n in xrange(requested_phone_numbers):             key = 'phone_{0}'.format(n)             self.add_field(key, validators.phonenumber(not_empty=true)) 

i don't think there's need call parent init