Odoo account_move_line rate

py

from odoo import models, fields, api

class AccountMove(models.Model):
    _inherit = 'account.move.line'

    currency_rate = fields.Float(
        compute='_compute_currency_rate',
        help="Currency rate from company currency to document currency.",
        store=True,
    )
    currency_rate_editable = fields.Float(
        help="Currency rate from company currency to document currency.",
    ) 

    @api.onchange('currency_rate_editable')
    def _onchange_currency_rate_editable(self):
        if self.currency_rate_editable:
            self.currency_rate = self.currency_rate_editable

    def _compute_currency_rate(self):
        super()._compute_currency_rate()
        for line in self:
            line.currency_rate_editable = line.currency_rate