Please who can help me.

This is my function to calculate some fields in the payslip but i dont know why its calculating them by steps and many times. Please help.

def compute_n_1_info(self,cr,uid,payslip,context=None):

nbr_mois = int(payslip.date_from[5:7]);

nbr_mois_anter = nbr_mois - 1;

print(nbr_mois_anter);

value = {'assiette_irpp_anuel_reel_n_1': payslip.assiette_irpp_anuel_reel * nbr_mois_anter,

'irpp_reel_n_1': payslip.irpp_reel * nbr_mois_anter,

'cumul_brut_imp_reel_n_1': payslip.brut_imp_reel * nbr_mois_anter,

'cumul_retenue_source_n_1': payslip.retenue_source * nbr_mois_anter,

}