I create this sequence:

sequence.py

    def create(self, cr, uid, vals, context={}):
        vals['code'] = self.pool.get('ir.sequence').get(cr, uid, 'res.partner')
        res = super(client_sequence, self).create(cr, uid, vals, context)
        return res

    _columns = {
        'code': fields.char('Code client', size=64, readonly=True),
}
    _defaults = {
        'code': lambda obj, cr, uid, context: '/',
    }

sequence.xml

<record model="ir.sequence.type" id="seqe_type_res_partner">
    <field name="name">Client code</field>
    <field name="code">res.partner</field>
</record>
<record model="ir.sequence" id="seqe_res_partner">
    <field name="name">client code</field>
    <field name="code">res.partner</field>
    <field name="prefix">CLT</field>
    <field name="padding">5</field>
    <field name="number_increment">1</field>
</record>

But the code is incremented by 3 instead of 1?? any help?