thanks but

  company_type = fields.Selection(string='Company Type',

         selection=[('person', 'Individual'), ('company', 'Company'),('external', 'Foreign')],

         compute='_compute_company_type', inverse='_write_company_type')

After adding the new value, if I select it it returns me to person

I think it's because of the method

_compute_company_type

Do you know how to prevent that from happening? I'm with odoo15

this is my workaround for this, I added  new a field is_organisme :

    company_type = fields.Selection(string='Company Type',
        selection=[('person', 'Individual'), ('company', 'Company'),('organisme', 'Organisme')],default='company',
        compute='_compute_company_type', inverse='_write_company_type')
    is_organisme = fields.Boolean(string='Organisme', default=False,
        help="Check if the contact is an Organism, otherwise it is a company or a persone")

    @api.depends('is_company')
    def _compute_company_type(self):
        for partner in self:
            if partner.is_organisme and not partner.is_company:
                partner.company_type = 'organisme'
            elif partner.is_company and not partner.is_organisme:
                partner.company_type = 'company'
            else:
                partner.company_type = 'person'

    def _write_company_type(self):
        for partner in self:
            if self.company_type == 'company':
                self.is_company = True
                self.is_organisme = False
            if self.company_type == 'person':
                self.is_company = False
                self.is_organisme = False
            if self.company_type == 'organisme':
                self.is_company = False
                self.is_organisme = True

    @api.onchange('company_type')
    def onchange_company_type(self):
        if self.company_type == 'company':
            self.is_company = True
            self.is_organisme = False
        if self.company_type == 'person':
            self.is_company = False
            self.is_organisme = False
        if self.company_type == 'organisme':
            self.is_company = False
            self.is_organisme = True

Hi Severin Caplazi,

1. First in your odoo addons find this field.

   2. create your custom_module in odoo and inside model.

   3. inherit res.partner model like this way,

  4. Then add below you modify field like this way.

here i add one (key, value) new as (test, Testing) you can add multiple here.

 5. Add this file in your init.py 

Thanks.