In below example, I have written Python script to loan/invest demand fields. Use below python code in your .py file :

 'date_start': fields.date('Start Date', states={'confirm': [('readonly', True)]}),
        'date_stop': fields.date('Maturity Date', states={'confirm': [('readonly', True)]}),
        'days': fields.integer('Interest Days', required=True, states={'confirm': [('readonly', True)]}),
        'rate': fields.float('Interest Rate (%)', required=True, states={'confirm': [('readonly', True)]}),
        'interest_payment': fields.selection([
            ('pre', 'In Advance'),
            ('post', 'On Maturity Date')],            
            'Interest Payment', required=True, states={'confirm': [('readonly', True)]}),
        'day_count_basis': fields.selection([
            ('360', '360'),
            ('365', '365')],            
            'Day Count Basis', required=True, states={'confirm': [('readonly', True)]}),
        'amount_main': fields.float('Transaction Amount', digits_compute=dp.get_precision('Account'), required=True, states={'confirm': [('readonly', True)]}),
        'amount_cost': fields.float('Transaction Costs', digits_compute=dp.get_precision('Account'), required=True, states={'confirm': [('readonly', True)]}),
        'bank_id': fields.many2one('res.partner.bank', 'Bank Account', required=True, states={'confirm': [('readonly', True)]},
            change_default=True, help='Bank Account Number.'),