I created a small module

class ProducctCottonPrice(models.Model):
    _inherit = 'product.template'

    cotton_qty = fields.Float(string='PCS in Cotton', digits=0, default=1.0)
    @api.one
    @api.onchange('cotton_qty')
    def _compute_po_id(self):
        for p in self:
            if p.cotton_qty <= 1.0:
                p.uom_po_id = p.uom_id
            elif p.cotton_qty > 1:
                p.uom_po_id = self.env['product.uom'].search([('factor_inv', '=', p.cotton_qty)] limit=1)

elif p.cotton_qty > 1.0:
 p.uom_po_id = self.env['product.uom'].create(
 {
'name': Cotton + ' ' + p.cotton_qty,
'category_id': p.uom_id,
'uom_type': bigger,
'factor_inv': p.cotton_qty,
'active': True,
'rounding': 1 / p.cotton_qty,
 }
 )
but if I have a product.uom_id.factor_inv = p.cotton_qty
It still do not pick the value and through me an error.
attributeerror: 'list' object has no attribute 'get'