Hi,

To create a list of clients and suppliers with a sequence number I made like this:

mymodule.py

...
class res_partner(osv.osv):
    _inherit = 'res.partner'
    _name = 'res.partner'

    _columns = {
        'n_client' : fields.char('Client Number', size=64, readonly=True),
        'n_supplier' : fields.char('Supplier Number', size=64, readonly=True),
    }
    _defaults = {
        'n_client': lambda obj, cr, uid, context: '/',
        'n_supplier': lambda obj, cr, uid, context: '/',        
    }
    _sql_constraints = [
        ('name_uniq_1', 'unique(n_client)', 'Number of client must be unique!'),
        ('n_supplier_uniq', 'unique(n_supplier)', 'Number of supplier must be unique!'),        
    ]

    def create(self, cr, uid, vals, context=None):
        if vals.get('n_client','/')=='/':
            vals['n_client'] = self.pool.get('ir.sequence').get(cr, uid, 'res.partner.customer') or '/'     
        if vals.get('n_supplier','/')=='/':
            vals['n_supplier'] = self.pool.get('ir.sequence').get(cr, uid, 'res.partner.supplier') or '/'
        return super(res_partner,self).create(cr, uid, vals, context=context)

    def copy(self, cr, uid, id, default=None, context=None):
        default.update({
            'n_client': self.pool.get('ir.sequence').get(cr, uid, 'res.partner.customer'),
            'n_supplier': self.pool.get('ir.sequence').get(cr, uid, 'res.partner.supplier')
        })
        return super(res_partner, self).copy(cr, uid, id, default, context)
res_partner()
...

mymoodule_sequence.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data noupdate="1">
            <record model="ir.sequence.type" id="seq_type_res_partner">
                <field name="name">number_client_sequence</field>
                <field name="code">res.partner.customer</field>
            </record>
            <record model="ir.sequence" id="seq_res_partner">
                <field name="name">number_client_sequence</field>
                <field name="code">res.partner.customer</field>
                <field name="prefix">C</field>
                <field name="padding">5</field>
            </record>
            <record model="ir.sequence.type" id="seq_type_res_supplier">
                <field name="name">number_supplier_sequence</field>
                <field name="code">res.partner.supplier</field>
            </record>
            <record model="ir.sequence" id="seq_res_supplier">
                <field name="name">number_supplier_sequence</field>
                <field name="code">res.partner.supplier</field>
                <field name="prefix">S</field>
                <field name="padding">5</field>
            </record>
    </data>
</openerp>

I get the numbering, but I have this error:

2013-04-15 12:41:07,379 4932 ERROR infinitechoice openerp.sql_db: bad query: ALTER TABLE "res_partner" ADD CONSTRAINT "res_partner_name_uniq_1" unique(n_client)
Traceback (most recent call last):
  File "/opt/openerp-7.0/openerp/sql_db.py", line 227, in execute
    res = self._obj.execute(query, params)
IntegrityError: could not create unique index "res_partner_name_uniq_1"
DETAIL:  Key (n_client)=(/) is duplicated.

2013-04-15 12:41:07,379 4932 WARNING infinitechoice openerp.osv.orm.schema: Table 'res_partner': unable to add 'unique(n_client)' constraint !
 If you want to have it, you should update the records and execute manually:
ALTER TABLE "res_partner" ADD CONSTRAINT "res_partner_name_uniq_1" unique(n_client)
2013-04-15 12:41:07,384 4932 ERROR infinitechoice openerp.sql_db: bad query: ALTER TABLE "res_partner" ADD CONSTRAINT "res_partner_n_supplier_uniq" unique(n_supplier)
Traceback (most recent call last):
  File "/opt/openerp-7.0/openerp/sql_db.py", line 227, in execute
    res = self._obj.execute(query, params)
IntegrityError: could not create unique index "res_partner_n_supplier_uniq"
DETAIL:  Key (n_supplier)=(/) is duplicated.

2013-04-15 12:41:07,384 4932 WARNING infinitechoice openerp.osv.orm.schema: Table 'res_partner': unable to add 'unique(n_supplier)' constraint !
 If you want to have it, you should update the records and execute manually:
ALTER TABLE "res_partner" ADD CONSTRAINT "res_partner_n_supplier_uniq" unique(n_supplier)

Problably I'm doing something wrong, do you know what it is ?

Thanks